You have to do it before you start the game.

All players have to come and log on the website.
A player has to open the game.
He selects the number of players : 3v3, 4v4 or 5v5, the mode : Team3, Team4 or Solo.
- 3v3 Team3 : Team3 VS Team3
- 4v4 Team3 : Team3 + 1 solo VS Team3 + 1 solo
- 5v5 Team3 : Team3 + 2 solo VS Team3 + 2 solo
- 4v4 Team4 : Team4 VS Team4
- 5v5 Team4 : Team4 + 1 solo VS Team3 + 1 solo
- 3v3 Solo : 3 solo VS 3 solo
- 4v4 Solo : 4 solo VS 4 solo
- 5v5 Solo : 5 solo VS 5 solo
If it's Team mode, he has to select his team and the opponent's one.
Then the Modes : NORM, AR, AR+H, EL, AR EL, CYO.
If you have some extras : HS, DM, CTF.
And the Creeps mode : Ogres mortal Satyrs Doom, Neutral, NCT, NCTS, Territory.

Your game is now notified and exists in the opened games.

All selected players have to come and agree with the starting game.

They can reach the game panel by clicking the "requested" icon.
You see the "log in" icon on the top right of the page ? When you have been selected for a game, because you are on a team, or as a solo player, this icon will show "requested" to signal you have to agree with the opened game.

You can enter an opened game only if you have been registered for that game, it means : if the player who opened the game has entered your name or selected your team.
All the selected players have to agree, if one cancels, game is closed without any warning.

When all players agreed, game status turns to "Now Playing", you can all go to Bnet.