If you have a current version of photoshop express, then the first option you will see on the opening screen is "open from adobe revel". You can tap on that and then sign in to select a photo to edit. After editing, hyou can tap the actions icon in the top right corner and select Adobe Revel to save the file back to revel.
Photoshop touch does not interface directly with revel. You would have to save the photo to your camera roll and then upload it using the revel app.