In Zen-Go there is only one group (" BW") for all players, so there's no need to build teams and you're done.
 
To play a game of Team-Go the game-master has to define the teams playing with each other.
 
To do that, on the "game-players"-page the game-master has to follow the bottom-link "Change color" or "Change color & handicap" (appears after all players have joined). Teams can be built using the select-box in the "Set Group"-column setting one of the following group-colors and submitting with "Save selected settings":

• B = black
  
• W = white
  
• G1 = group #1
  
• G2 = group #2
  
• BW = black and white (only used for Zen-Go)
  

The group-colors 'G1' and 'G2' can be useful to setup a certain team of starting players for Team-Go without setting a particular color of black or white yet.
Setting up teams before finding other players can be useful to give other users a chance to see against whom they have to play, or they can ask the game-master to be put into a specific team. Though it's optional to setup teams this early.
 
The game-master can change the teams at any time before the game is finally started. However, before the game can start, the colors for all players must be set to either 'B' or 'W'.
 
When all required players have joined the MP-game, the average ratings of the teams are shown as well as "Group ratings", which can help in choosing a fair team structure with balanced strength distribution. If all players joined, it's also possible to choose the handicap stones and komi for the MP-game.