I am in the process of learning too, and this is what I have gathered.
Learn Your Class: It sounds simple but knowing your class/spec inside and out is crucial, especially as a dps. Knowing what CC dr’s with other CC, and what spells you cannot CC during, are really good beginner steps. SkillCapped offers some really detailed videos on YouTube that are worth checking out. Your class discord should have a PvP section littered with content, tips, and memes.
Addons: Personal preference, but GladiusEx or sArena are pretty much a staple for any and all PvP players. Others like Bartender and WeakAuras can be used to put your CC/cooldowns into a more visible spot. OmniCC tracks enemy cooldowns right out of the box. Those are all to your discretion though.
Find some friends: This is where I am struggling. It can be rough finding people to consistently queue to get games in. If you are trying to climb ratings, it is preferred that you look for people who are above your current rating rather than below. I form my own groups for this.
Abuse your class: Goes back to learning your class. Sub is pretty easy to grasp and more than likely your best option. Off meta specs are fun to play but unfortunately it is sometimes better to play to your strengths rather than your weaknesses. Rogue/Mage/Priest or Druid or Pally is an incredibly friendly comp for someone to learn.
Watch streamers/YouTubers: Although some streamers are not fond of offering advice, a majority will. The really top end players with a large viewerbase have a harder time seeing your questions, and the viewers can/will be just as lost as you. Some do offer YouTube guides so those are always worth checking out.
This is my first serious season and I am at 2.1k 2s and 2k 3s, both with 2.3k mmr. I am trying for the gladiator mount though.
And to answer your questions, you can play 2s, 3s, or RBGs if you want the vicious PvP mount. If you want the gladiator mount, you need to queue 3s.