The Game Trials decides who will enter The Game. Normally, only the winner enters The Game but because of Bloody Mary's entire group being kick out of The Game, the most recent Game Trials selected the top 5 players. Jane (Bloody Mary) was the leader. Kleya Smith was second, followed by The Bandit, The Dude, and Waterman. Waterman was then kicked out of the group, allowing Danni to enter The Game.
It is a double elimination tournament, with 32 teams. Each time has two players, so there are 64 competitors. Each round is timed (3 minutes) and begins with a period of time when specials are not allowed. For most battles, this period of time is 20 seconds. In the finals, there is only a 5-second special blocking. HP is halved, and only one special is allowed per competitor.
If the time limit runs out without someone losing, then the fans get to vote for the winner.
Apparently, most people who enter into The Game through the Game Trials are citizens. We can see this because the announcer of Jane and Kleya's battle said that both finalists being Outsiders is a first in the Game Preliminaries.