A Relocation Ship is used to move a base from one planet to another.
To move one of your bases click the "Move Base To New Planet" button on the Command Relay or Central Processor .
From this dialog you can use tritium to bring any buildings from your current base.
If you do not use any tritium you will be starting a new base with just a Command Relay or Central Processor .
Any buildings you bring with tritium will build instantly through your constructor when you build your new base.