iOS is, generally speaking, easy to use, but there are exceptions. Determining how to add photos from a Shared album to an existing Photos library isn’t especially intuitive.
Let me explain. Saturday was the two-year birthday party for my granddaughter, Elizabeth. Family members took lots of photos and published them in the “Sharing” section of the Photos app.
I wanted to move some of the pics to a photos album I created and dubbed “Elizabeth’s Second Birthday in my Photos library. It’s easy to do this on a Mac; you can just drag and drop. However, when I selected photos in iOS’s Photos on my iPad, there were options to Airdrop ‘em, email ‘em, Message ‘em, etc., but no obvious way to simply implement an “add to album” option.
Instead, as I finally discovered with Steve Sande’s help, with iOS Photos, you must open an album, tap Select, and choose Add (at the top left side of the screen). Then you can select items to add to an album.