Pick your poison game mode.
5 v 5 Your team picks a 15 champion pool for your opponents and they give you your 15 champ pool.
Fist person picks 5 then their first picks your 5 then back to your team that picks 4 and so on till all 15 champs have been picked.
You can not give the same champ to the other team as a champ that is in your pool. So when both teams are done their will be 30 champs slected out of the 100 plus pool. And only 15 champs to build a team from.
I pick
---------------------------------They pick 

The champions I picked are not used that often the champions they picked have really difficult mechanics so if you have never play with them you can gat run over but if anyone on your team mains one it could allow you to shut them down the next person would pick four champs so they could give them champs that are bad vs
or
then they give us champs that are bad vs
and
. they could we could end up with only
as an adc with no support and they have
and
.
You pick the champs you want to fight and see if your poison kills you or if the other team poisons them selves. pleas riot.