I guess it's the same in both (I have only experience with LoL), but you can play with any combination. The "real" game is usually 5 vs 5 people, 5 people vs 5 bots is used for training.
And then you can make a custom game with friends (be in the same team or different teams) and fill in the remaining roles with bots... or just play 1 vs 1 if you want.