Once you are happy with your collage, you can save it as a TurboCollage Collage Design Project (.turbocollageproj) file that can be opened later using TurboCollage to edit your collage. You can also transfer .turbocollageproj file to a different Mac and edit it there as well.
Use Save/Save As from the File menu.
Save TurboCollage Collage Design Project (.turbocollageproj) file.
Note that you can email or use other means to transfer .turbocollageproj files to a different Mac and edit your collage there.