Hi DarlinJacq usually when you tag a photo it means that the person tagged is in the photo. When you tag the photo then the person tagged is notified and they get all of the responses and comment notifications for the photo too. Some people use the tag feature when they want you to see a photo though, so you might get tagged and not be in the photo.
Tagging a photo on Facebook basically means linking a person, page, or place to a picture you have posted. This is a popular method of online photo sharing when can also identify people in the photos. When tagging people link every face with a name which is mostly the name of the person on the photo.