That’s the neat part- you don’t! At least that’s partially why I’ve given up on it. (I missed having IRL folks to dungeoneer with.)
I also wish the addons were not so necessary. WeakAuras, DBM, IO, and so-on-and-so-forth.
Why aren’t these things already built-in? IO kinda is, but the rest you’ve gotta install to be remotely competent, especially at higher levels.
OP this is a great little site with good information on m+
^This 100%.
Technically base is 1 not 0 hence there are no 1s.
Excellent reply, well done on explaining in a way that didn’t require the reader to already know most of what they were asking for an explanation of.
I dropped WoW at the end of Cataclysm and came back in late BFA but didn’t get into endgame before SL released. When I was raiding in SL I was dimly aware that some people I raided with were gearing up outside of raids using a “mythic plus” dungeon mode but had no idea what was involved in that. When I tried asking how it worked, I consistently got vague not-actually-an-answer responses from people who couldn’t understand that it was a game mode that hadn’t existed last time I was in endgame mode. Advice like “just start in 2s and work your way up” means nothing to someone who needs to know where to get a key and what to do with it! Your post is exactly the kind of answer that would have helped me back then.
So can you just run all the 0’s every week for gear or once you get a key from a 0 you have to move in to the + stuff that has no lockout?
Watch vids and routes; learn your rotations and how to do the mechanics.
Start at 2’s and move up.
If you need to, use your own key, and burn it back to a 2 if you don’t feel comfortable advancing yet.
I suggest getting as many dungeons done at lower keys to start your IO journey, then queue for higher keys or run with guildies.
The more IO you get, the more the groups will be willing to take you along moving forward.
While I’m certain you’ve already got your questions answered as this is a really great post with explicit questions, I’d like to offer up some advice.
M+ is a community game unless you’ve got dedicated groups, and often stronger players will get frustrated at weaker players. It is fine to be frustrated, but please aim to be constructive of others even if they are unsavory, as the people who do bolster randoms and bads are the people who grow the M+ experience to be better for all.
Secondly, blame in M+ tends to stand out like a sore thumb, if you’re not already used to it, practice being humble. Often, non-healer roles will incur hits from stuff in their control, dip low, then die from unavoidable items and blame healers. DPS will face pull or accidentally pull something, and blame someone else whether by lack of awareness or shame.
The BEST way to experience M+ in any serious capacity is going to be besting yourself and your habits in relation to the content. Own your mistakes, especially if you PUG, as everyone makes them and you can’t ever control what others are doing but you can control yourself in the future.
If you go into M+ with the right mindset, even busted keys or keys that fall apart will offer you some way to grow and push yourself as a player if you let them.
It’s important to reflect on your play when you play poorly.
It’s even more important to reflect on your play when things go great.
You can keep doing M0s if you like. Though if you can do an M0 comfortably, you can do a +2/+3 comfortably.
While a 2/3 will only give up one piece of gear per dungeon and at the lowest rank, you can still upgrade this gear with valor points if you really need to. I would advise you hoard up valor until you cap and get into higher keys.
But more importantly you’ll get great vault progress, which helps your ilvl grow a bit faster or for you to get tier if you don’t raid.
A player who just spams M0s will end up at 372
A player who just spams +2s will end up at 376 eventually from dungeon drops and 382 eventually from Great Vault. As you can see, it’s worth doing at least 1 to 4 keys of the highest you can hang with to get your gear up early
Clear an M0 get a key and then run it. Or hit I, go to premade and register for the keys you feels most comfortable completing.
Im ilvl 378 and the only mythic plus dungeon I want to do is the academy…what would be am appropriate key lvl?
I checked out my Vault last night and in addition to the Mythic unlocked rewards, I got a M9 key for Academy!
Is the Vault Mythic key reward random? Or based on your progress?
The biggest thing to note here, since a dozen people have explained the basic M+ system, is to remember that in M+ gear will only get you so far.
Having 405 ilvl is good enough to do pretty high keys, but you arent going to just roll into them. IO score is all well and good, but whatever your roll in the key is, dungeon knowledge and experience in M+ is extremely valuable. As a raider, you might find you need to use skills and abilities you normally ignore. Knowing what you can do to mitigate enemy mechanics is basically required in anything over a 15 and probably before then.
The catch is that staying in the very low key range for too long will be a bad idea because you likely wont learn anything.
Best way to learn is to play with a similarly geared and skilled group and push the hardest stuff you can. Getting carried, either by your gear on low keys or by far better players in higher keys… wont help you.
Final tip - as DPS you might need to do a variety of things depending on affixes, dungeon, trash pull, boss, group comp etc. Get familiar with interrupts, anything that might stop a cast, and any personal defensives you have… and then use them.
Its always scary doing an activity for the first time. I can assure you it’s not as bad as the horror stories make it seem.
To answer your question of where you get a key, you run any mythic dungeon, including M0, to retrieve your first key. You will loot a key from the last boss in the dungeon, and what you get will be random. There are 8 dungeons you can get currently, refer to your dungeon journal in-game for what is active this season.
Once you have your key, create a dungeon group and list what level your key is. Most people keep it simple by just saying “+2” or whatever key you’re planning to run.
Your group will then assemble at the dungeon, insert the key into the keystone font (once everyone is ready of course) and attempt to complete it to the best of their abilities. Tip: it is considerate if you do a pull timer before starting the key. It gives the group the last few seconds to prepare.
Depending on how fast you complete the dungeon will dictate how much your key difficulty will increase, up to a maximum of +3. If you don’t time the key, your key will simply lower in rank by -1 but can never go below level 2.
As your key increases in rank, so does the difficulty and challenges you’ll face. You will quickly notice there are ‘affixes’ you need to contend with. These affixes is what makes M+ interesting because they change every week. An example of one is Sanguine. When an enemy dies, it can leave behind a pool of blood that heals their allies and damages you.
I would recommend watching a beginners guide on youtube to best prepare yourself.
Wishing you the best of luck and may the keys be in your favour. 
YouTube or google your m+ spec - mage-hub.com if you are a mage. Then apply the rotation they describe to a target dummy until you remember it. After you do m0 you will get a key usually a +2 or something. Then you can open your group finder and start a group or join one. This is where you use the rotation you practiced. Keep in mind, some guides might not describe interrupting mobs until you get to higher keys 15++. If you are doing 15s, I would hope you know how to interrupt by then but a lot of people in LFG do not understand this. Good luck.
You should be using interrupts all the time. It does not matter the difficulty of the dungeon, or even whether you are in a dungeon at all - if you have an interrupt, and the enemy is casting a spell you can interrupt, you should interrupt it.
In higher difficulty keys there will be some caster enemies with “filler” spells and “dangerous” spells. You’ll want to save your interrupt for the “dangerous” spells, and you’ll learn which spells those are as you learn the dungeons better.
I always do a delayed interrupt.
I wait until the bar is +50% in case someone else blows theirs first.
Do a mythic 0, get a key and create your own group using the lfg tools.
Or using the lfg tool, find a mythic 1-5 and request to join. Your ilvl will get you into the casual mythics, np.
World of zergfest.
I always interrupt where possible and it makes sense, but I swear many wow players don’t even have it on their bars.
Just use the group finder and start joining groups. Any key that is +9 or lower should be a good time (probably start with a +4-6 key if you can find them, no need to start with a +2). Keep practicing. Learn the dungeons the best you can. Start by running them and if something is confusing, check the dungeon journal. It’s understandable to feel intimidated, but you just gotta get in there and start playing.
Don’t worry so much about your damage. Read everything. Buffs, debuffs, information on your interface. Even if it costs you a bit of damage. Once you are familiar with it, you will know what is going on and can work on damage.
Identify your tank and follow him. Maybe throw a mark on his head. Let the tank pull and kill what he pulls.
As a hunter, in a mythic plus dungeon, you are expected to:
Cast misdirection on the tank. Just use it between every pull is a good way to start.
If no other class has bloodlust / heroism you are expected to have a pet that can use that. A good way to start is use it on every boss, if it is available.
If you run into toxic people, you don’t need to interact with them. Also, once you are about to start the dungeon, you can say something like “haven’t done much m+ this expansion, feel free to give me tips” and that automatically will help remove negativity and you might get some on the fly advice.