Zombie Manic Mini Game
The team selector is a process that can be accessed by selecting the book item (menu) from your hotbar in the lobby, this will open the main menu, where one of the options is select a team:
You can either select Humans (selected for you by default) or Zombies. If no player chooses the Zombie team, a random player is chosen by the random generator. If multiple people choose zombie, the server will pick as many of them as needed to meet the human to zombie start ratio, and the rest will start as humans. We typically have this set at around 1 zombie for every 3 humans in match.