I would realy appreciate some help

Edit: I should have mentioned that I am returning player, which I didn’t mention because I’m returning after such long time that I don’t remember what I’ve did in the game back then or what should I do now.
I can only assume that I already moved through new players matchmaking into regular one and that’s why I had so much difficulty keeping up with my starter deck.

It was also after I’ve made this topic asking for help when the game offered me free deck to play with which I gladly accepted.
Did I made good choice when I picked Lightforged Retribution? I’m kinda confused by those mech cards. Was Uther Lightbringer an engineer?

Jokes aside, only thing that I know for sure is that I should reach level 10 with each hero. Other than that I’m completely lost.

Edit: This only proves how confused I am after returning to Hearthstone after such long time and being treated as if I know what I am doing.

If I decide to spend money on Hearthstone, which hero is beginner friendly and which packs have highest chance to contain easy to understand yet still viable to play cards.

Original: Hi, I would like to ask few questions about this game.

So far I somehow got the basics, built starter deck, defeated Innkeeper several times to got those heroes you can unlock in practice mode and then I tried play mode against other players only to get obliterated every single time by more experienced players with deck build for advanced strategy play with cards from various expansions.

I assume that matchmaking is not expecting novice players with starter deck built of classic cards and It was extremely foolish to even try playing against other players.

What should I do now then?
Shall I just keep playing practice against Innkeeper? What should I have before even attempting to run other solo adventures besides practice and which one I should focus on?
Also what is the best way to learn how to improve my starter deck into something more viable?

Thanks in advance for all the tips you can provide.