Trying to provide you with the best game experience, we use the following approach to always have a world with what you built (the BuildWorld) and a world where everything is generated using the latest version of Minecraft so where you can enjoy the latest content (AdventureWorld).
When you first join, it is your decision where to go. You can go right into the AdventureWorld, explore newest content, build and claim there. But beware! Every time a new Minecraft version where new content will be generated is released, the old AdventureMap will be removed, including your claims and buildings – just everything.
So, if you go to the BuildWorld, this world will always stay, but doesn’t feature the latest content. This means, if you head out to the AdventureMap, you should build yourself a home (/sethome <name-of-home>) in the BuildWorld sometime. Especially the prettiest or most-afford-buildings, you should build there (in the BuildWorld).
To switch between worlds there are portals at the spawn. You can use them to teleport to the different worlds. Then do a random teleportation if you want. This random teleportation will randomly teleport you to somewhere on the map you are on within a specific radius around the spawn.
To make it easy to collect new items and bring it to your home in the BuildWorld, you can for example go to the AdventureWorld, collect things. Then type “/home mycoolhome” to return to your home in the BuildWorld. After you put the things you collected into a chest, just type “/back” and you will be teleported to where you were at on the AdventureMap. If unsure, you can also set homes on the AdventureMap.