Xcas may open different sessions, each with its own levels. You can move levels inside a session or copy a level from one session to another session.
To move one level in the session, press the mouse on its level number and release it at the destination. If you want to move some contiguous levels, click on the first level, then shift-click on the last level (that is, click on the mouse while pushing the shift key). You can now move these levels by pressing the mouse in the selected area and releasing it at its destination. You can also copy these levels to another session by Ctrl-C/Ctrl-V or select/middle click.
You can delete the selected levels. You can paste the selected levels elsewhere by clicking with the middle mouse button on another level number. You can merge the selected levels in a single level. You can also group the selected levels in a section and give it a section name, sections may be folded or unfolded.
The File menu of a session will let you save/export/load/import
a session in/from the current session. The Session menu
from the top menu will let you insert a new session.