Help/Advice for (Somewhat) new player.

I've been playing LOL for 3 days now and I'm level 9. Even when I started I wasn't bad at the game, since I had a past history with DOTA 2 and Paladins. DOTA 2 was extremely complicated and toxic, so I only played with bots, hoping that I could improve enough to be able to play in a real match someday. I spent over 50 hours in bots, then, getting bored, I gave up on the game. Then I found LOL, a much better game. My experience from Dota allowed me to learn and advance in LOL quickly. I knew many basics already, such as ganking, last hitting, etc.

Here's where I need help.

In LOL I don't know much about the actual champions, their roles, their abilities, strategies, etc. I need some tips or some guidance for what champions I should pick in which situations, and I also need to know some answers to basic questions:

What does an AP Damage mean?

Who would be the best champion for someone like me? (I currently use Annie and Malphite as my "mains". I've been getting S ranked grades with Malphite, so he's really good, and any advice for him would be appreciated. I normally don't main in any game, rather I choose any character based on the circumstances, but I don't have enough IP to be able to purchase more champions. I have 1072 after purchasing Annie and Malphite, but if I have to buy a new champion that costs 1350 I can play enough to get that champion.)

What are the roles in LOL? (I heard stuff like tanker, top laner, mid laner, bottom laner, jungler, etc. I know some of this stuff, but not all of it. And the stuff I do know is kind of incomplete.)

Which champions of LOL are currently in the meta and extremely powerful?

Which champions of LOL should I not play as?

I don't have any friends that play LOL, so can you suggest any champions that are good as solo? (It is rare for me to experience a friendly player who actually listens and cooperates. I experience a player like that one every 5 games or so. Which means that most of my games are gonna be bad if I rely on the rest of my team. I don't mean a champion that is OP in 1v1 and horrible in team fights. I mean a champion that can hold his own with enough damage and durability while being able to help the team at the same time in a team fight, because from experience, a team fight happens basically every game, and if I'm not ready for that then it could lead to a loss. Annie is amazing in 1v1 and can even survive in 2v1 under some circumstances but isn't that effective in team fights.)

There might be some more things that I might not know about LOL, but I'll learn that along the way, as I advance and gain more experience. For now I need to complete my basic knowledge.