If you mean you have different maps that you want to load and unload on command and in various combinations, Streaming is what you are looking for.
If you always want one level at a time, use the simplest Open Level. Just be aware it’s the simplest and least supported system, with little exposed control.
If you are making an open world with vast exteriors, use the new World Partition system.
I also worked on projects with a mixed Streaming and Open Level approach. Different big levels were opened with Open Level, while their “chunks” were streamed. I don’t recommend it, though—you have to handle two systems at the same time.