After you’ve created your collage, click the Done button up the top right of the screen. You can then edit the photo within our editor (add Text, apply Filters etc), and finally when you’re ready click Save up the top center and then the red Save Photo button.
If you have a registered Ribbet account, you can download the photos from your phone by visiting ribbet.com/mylibrary?dld=1 (on your phone’s web browser) and signing in with your account details. Another option is to email the photo to yourself from your desktop/laptop, and then check that email on your phone. Or, you can save directly to Google Photos from Ribbet and then access them from your phone.