All worlds can be accessed by any player at any time.
“Vanilla” worlds including the overworld, nether, and end can be accessed using the portals at spawn or by using a constructed nether portal or naturally generated end portal after inserting all required eye of ender. All players have permission to break, place, and interact in these worlds. These worlds all share the same inventory, enderchest, and exp.
The creative world can be accessed exclusively using the portal at spawn. Only platinum members can claim a plot which will allow them to break, place, and interact within their plot(s). A platinum member can however add any player to their creative plot. These added players will be able to break, place, and interact within the plot as long as the plot owner remains online. The creative world, for obvious reasons, has its own inventory, enderchest, and exp which cannot be transferred to any over the “vanilla” worlds.
For more information on the creative world, visit: https://support.liveandbuild.net/membership/creative-world/