You must In order to edit a photo it must be part of a collection. In order to be part of a collection it must be:
1. Part of a Lightroom desktop collection synced to Lightroom mobile.
2. Part of an iPad-originated collection (say from Camera Roll) that is syncing back to a Lightroom desktop
Lightroom mobile will require you to: Log in using a valid Adobe ID (30 day trial only for non CC IDs) and then ask you to Sync to a Catalog on Lightroom Desktop that is signed in and syncing. So, you can edit images which originate on your iPad, but understand that they will sync back to your desktop as soon as you log your LR desktop in.
You don't need to sync photos from a desktop first, you can edit photos you took with the iPad camera. This article describes how you can set up Lightroom Mobile to to do all that and then, as Rikk said, the next time you sync the photos will go automatically to Lightroom on the desktop.
thx rikk & conrad - that's helpful and conrad's link makes clear how in a pinch to use iPad as a camera, use LR on it, and have it available later on desktop. this makes the mobile LR more attractive to me.
Now, I'm a bit confused. I've set it up. The synch seems to work on new images from iPhone and I can select from my existing photo roll on the iPhone. I then did two edits on one of the latter already synced images on the iPhone. I hit sync with each. Trying to get back to the original image I inadvertently seem to have synced on a third edit. I'm not sure I ever got back to the original (no clear undos in LR Mobile). But when I checked LR on desktop and clicked on the image initially I got the third edit which blinkered out and was replaced by the original photo. None of the edits showed up on the desktop. Either the program is still buggy or there are limitations on (a) saving both original and edits, much less multiple edits, on the iPhone and (b) syncing edits back to the desktop.
I think LR Mobile needs better documentation, instructions, or what have you.
Haven't tried on an iPad yet. I've got another question on that which I'll raise in a separate question about controlling syncing (orums.adobe.com/message/6628267#6628267).
bottom link should be to forums.adobe.com/message/6628267#6628267
try again: forums.adobe.com/message/6628267