The done menu appears when you have completed editing your photo. It consists of several options.
Compare allows you to review the before and after of your photo. It can be accessed in the save menu by selecting the compare icon. It can also be accessed by placing three fingers on the display. Lifting your fingers will return to your currently edited photo.
Add preset allow you to save the edits that were made so they can be applied to future photos.
Save will save your edits to your photo library on your iPhone or iPad.
Share will allow you to share your photos with various social media services and other apps on your phone.