You will have to clear both Customs and Immigration at JFK. After Immigration, you will collect your checked baggage and go through Customs. If the check-in agent at Heathrow has checked your baggage through to ORF, then just after clearing Customs at JFK, you should be able to drop your bags at the re-check station. All AA mainline and American Eagle flights use Terminal 8 at JFK.
On the return, AA should be able to check your bags all the way through to LHR, and you will not see them again until you claim them at LHR.
To get from Terminal 8 to Terminal 7 at JFK, you will take the "All Terminals" Air Train one stop. The ride is free, and should take all of two minutes. (Make sure that you board the correct AirTrain: do NOT board one bound for "Jamaica" or "Howard Beach.")
You will have to clear both