Saving the scene
Saving the scene is pretty simple - just press Ctrl+S or choose File -> Save from the main menu.
This will save a file that R.U.B.E can load again to return the scene to the current state and
continue editing later.
To save a file that you can use in your own program, it's recommended to export a 'raw info' file.
This can be done by selecting File -> Export -> Save raw info from the main menu.
More about using exported data.
Saving with the trial version
The above methods are not available in the trial version, but you can use script logs
to avoid losing any work you have done.
More about script logs.