7 mile beach is the best beach for sure, and it is all good just grab a taxi and have the driver drop you at a public entrance to the beach. It is free that way. Hotels usually charge a few dollars to enter the beach from their property.
exactly what the others have said. 7 mile beach is the beach. You can go to the public beach or you can use the hotels beach for a fee-which entitles you to use the hotels facilities. There are lounge chairs to rent and vendors all along the beach.
There is also "Rum Point", which is on the other side of the island, very pretty beach and some good snokeling. I know they have ship excursions there or you can just take a cab.