This ^^ Only things that cost money are skins.
You can buy characters for real money or buy them with IP (in game currency) that you get from playing games. Theres 15ish free champions that you can play every week and then they change it to another 15 random champs. So you play these until you get enough points to buy your own. Usually 3 games will get you a cheap champ where the expensive ones take 60ish games if you win a lot to get. They are all very balanced as well. The whole game is very very balanced which is why I love it so much.