Since your question is about Photoshop for iPad, I have moved this from the Photoshop forum where you posted.
You can open one photo at a time and the saves are automatic when you close. You can't close without saving. Use Undo and/or work on layers and be sure the file is as you want it to be before quitting the application.
Hi Jane, I don't think that's right. For example, try opening a photo from Photos in Photoshop, work on it and then quit Photoshop. The changes are not saved in Photos. Also, how do I switch between multiple open images?