Zandvoort (nowadays also marketed as Amsterdam Beach) is the beach town that is the closest to Amsterdam. Basically, the entire North Sea coast is one large (about a 100 miles) sand beach, with fine white sand.
Beaches in the Netherlands are freely accessible, you don't have to pay a fee.
This beach can be accessed on many locations, and Zandvoort is the most practical place for most Amsterdammers: from the Central Station, Zandvoort is an easy half-hour train ride.
And the train drops you off almost right on the beach - the Zandvoort train station is just a minutes' walk from the beach.
Trains go a few times per hour, every day of the year, from about 6 am to midnight. Check ns.nl for details.
(TIP: if your hotel is close to Amsterdam Sloterdijk, it is faster to get on the train on train station Sloterdijk).
In Zandvoort you can find various shops and restaurants, also along the beach boulevard.
TIP: trains to Zandvoort stop also in Haarlem. This is a nice old town, with many shops and restaurants, which you may include in your daytrip.
North Sea beach
Sunset at Northsea beach