Creating Tags and Objects in Parse (backend service)

Creating Tags and Objects in Parse (backend service)

I am creating an ios app that saves Photos and Comments, specific to a
current String. These images and comments should get saved to Parse, and
later all retrieved using the String as a tag.
How can I create a Tag object? which has properties image and comment.
How can I save image and comments particular to that string?
How can I retrieve these images and comments in my app when that String
comes up on display?