Coastal destinations are served by bus and train, but the interior is sparsely networked. Away from the coast, having your own wheels helps.
Driving and cycling routes are abundant; highlights include the coastal Corniche des Maures, the Route des Crêtes from Bormes-les-Mimosas, and the roads in the Massif des Maures and the Haut-Var.
Driving into St-Tropez at high season can take hours, even before struggling to find a park. It might best to arrive by boat, especially if you move in yacht-owning circles. Presuming you don't, Trans Côte d'Azur runs scheduled ferries from Nice and Cannes between May and October, or there's the sea-taxi from Porquerolles (which will set you back a cool €1000).