A SpawnLocation is a BasePart that will act as a location where the players will spawn.
If no other actions is taken, a player will spawn on a random SpawnLocation that have the setting Neutral set to true. If the player is in a team, the player will spawn on a random SpawnLocation with the same team color.
If the Players.AutoSpawn setting is false then players won't spawn automatically, but a call to:
Player:LoadCharacter()
Will make the player spawn on a random spawn as described before (this code can also be used even if the AutoSpawn is true).
With the teleportation you can make a player spawn on a specific spawn in another game. This spawn is targeted by using the spawn's name in the teleportation code. The targeted spawn must have the Neutral value set to true tho.