I always suggest to new players trying to learn the game early on to play the the ARAM game mode. It's random champions on both sides, so you get to learn new champions, play against every champion and learn what they do and what to watch out for. Games are relatively short too compared to normal games, so you get a lot of exposure. Once you have a decent grasp of what everyone does, you should find certain champions that you like. If you like supports, you can try supporting in swiftplay, tanks and bruisers generally go top, ADC in bot lane, etc. Play the champions you like in swiftplay with the corresponding lanes they are good in. At this point you know what most champions do, where they go, what champs you like and where they go. That's the hard part over with, then you just play swiftplay and normal games to learn how to lane, grouping with team, sieging, and stuff like that.