Just notice this in the help section of the client.

Banning Champions Each team captain chooses two champions they wish to globally ban. A "global ban" means that no player, regardless of which team they are on, can choose that champion during the upcoming champion selection process. The bans are chosen in a 1:2:1 format, meaning the first team chooses one champion to ban, the second team chooses two champions, then the first team chooses the final champion.

How old is this Rito? :D