Traveling with train from Frankfurt Airport?

I apologize for asking here but I can't seem to find the proper contact on the DB site. So if someone knows the answer I'd really appreciate it. My parents will be traveling to Germany. They will arrive to Frankfurt airport (the main one, not Hahn) and then continue their journey by train. On the DB site there are so many different options available, I don't know which one to choose. Some are obviously the same thing, but others are different and have different time tables. Does anyone know which one you have to look at?

At the DB site, the following options are available for Frankfurt Airport.

Frankfurt am Main Flughafen Fernbahnhof

FRA Frankfurt Airport

Frankfurt am Main Flughafen Regiobahnhof

Frankfurt - Flughafen, Flughafen Frankfurt am Main

Frankfurt, Flughafen Frankfurt am Main

Frankfurt(M)Flughafen

Frankfurt(M) Flughafen Fernbf

Frankfurt(M) Flughafen Regionalbf