[2020] New League Player - confused how i'm meant to learn the game

I am a 98th percentile DotA2 player so I guess my mechanical skills and awareness is okay enough... I recently thought i'd give League a try, my issue is that in most games I just have NO clue what the enemy champs do, abilities, runes and whatever. I would love to go into a lobby and try them all but I haven't unlocked these champs so I believe I have no way to learn them? Am I doing something wrong or is there no way to go into this game with any knowledge of how anything works?
Sorry for ranting but I think I'm too new to understand how to learn to play this game at this point.