When the game starts in Play Mode, players will all spawn at the Initial Spawn Point. You can use a Wrench to switch between different Team Initial Spawn Points.
Place this tool in the location where the players gather when the game starts, if the map has a countdown then after the countdown all players will be teleported to that location point.
For PVP maps that have teams then use the wrench then click this tool to set which team will be teleported to this point.
When using a wrench, this tool will change colors sequentially: