This plugin is quit simple, it just do so then you set a spawn, it's locked to that world. So if you are in nether, and type /spawn, you will be teleported to that spawn that is set to nether. If there is no spawn for that world, it will teleport you to the default spawn, that is the FIRST spawn you hae set on the server.(this will be change soon, so you can use /setDefault to set the defaultSpawn.)