This article describes how your work is automatically saved to your Hub. 

See Export if you need help downloading images to your computer.

Images are automatically uploaded to your Hub

When you select an image to edit, before it is opened in the Editor, it is automatically saved to your Hub.  

If you've wondered what exactly is going on here: it is the the two step process of uploading the image to your Hub and then loading it into the editor. 

Changes are automatically saved as you work

If your document in the Editor and Hub are in sync, the save status in the top right, next to the image's name, will be green. 

If this little circle is green, your work is saved. 

Unlike opening the image, updating  happens very quickly. You might be able to catch a flash of yellow-orange in the "save status" at the top right of the editor after you apply an effect or move a graphic around. Typically though, updating changes to Hub is nearly instantaneous. 

Make a Copy when you don't want to write over your past work

When you want to work on an image, but aren't sure you're ready to commit to changing what you already have, select "Make a copy" near the top of the editor. This will copy the work in it's current state to a new file, and load that file in the editor: preserving what you've already done as a separate image. You can do this at anytime while you are editing. You can also opt to Edit a Copy before you even get into the editor. For more on that see opening image you've worked before.