Help with editor!!

[BLANK2042]

hello i have a basic question on the hpl level editor, i have been openeing other peoples maps in the level editor to try and learn more about the editor and such, so i loaded the french map about the prison, and the only area is the prison that i can access, i was wondering if theirs a way to open a new tab or page or something to see the rest of the map (also to give my map another "level"), on the french map theirs an 'area' that is level change, but i dont know how to see the rest of the level, or to create multiple levels in the editor.