How do you get from Philadelphia airport to NJ beaches?

Since your question was in the Bus and Train category, I'll limit my responses to that. From the airport, you should take the R1 airport line to downtown Philadelphia. The train will stop at 30th Street Station. Here you can transfer to the New Jersey Transit Atlantic City rail line. If you want to go somewhere other than Atlanic City, stay on the R1 until you get to Market East Station (two stops after 30th Street). From there, you can walk over to the Greyhound bus station at 10th & Filbert and hop a bus to any of the shore towns.