The closest beach to Hollywood, California is Hollywood Beach—located in the city of Hollywood, Florida. This is a common point of confusion.
If referring to the Florida city: Hollywood Beach features a famous broadwalk (not boardwalk—it's paved for cyclists/pedestrians), Charnow Park, Garfield Street paddleboard/kayak launch, and the historic Hollywood Beach Resort (Margaritaville). It's a major destination in its own right, not just "the closest beach."
Santa Monica State Beach (~7 miles) offers the iconic pier, amusement park, and Muscle Beach. Venice Beach (~8 miles) has the famous boardwalk, skate park, and canals. Dockweiler State Beach (~10 miles) allows beach bonfires and has RV parking.