On the surface, saving your level seems like a simple process; however, there are a few important functionalities that you should be aware of when saving your level. This recipe will show you how to do a basic saving, copying/moving your level (do not use Save As), and auto backups.
Have any level open inside Sandbox.
Open Windows Explorer to the following location:
To save a level, go to File | Save.
Ctrl + S does not work by default. You will need to set up a shortcut key yourself for that.
When copying/moving levels: