Ofcourse you have champs that counter certain other champs but for that you have blind pick. Meaning you won't know what you're up against untill after you chose, this is how most random games are played. If it's about ranked (the actual stuff that matters for most) you have to be lvl 30 and have a certain amount of champions. I talk about lvl 30 because when you reach that lvl you should have accumulated enough ingame currency to buy the champs you need. That + the free rotations should be enough for you to play at least 1 position and poses picks and counterpicks. There downside about league is that they're constantly reworking champions and while they rework them they usually don't get more balanced...at first lmao.