Coming from the north, you need to follow the directions for Napoli (Naples). From here you need to take the Autostrada A3 (motorway) and follow the directions Napoli - Pompei - Salerno, exiting at Castellammare di Stabia, and follow the signs for Sorrento.
You need to arrive preferably at Naples airport (Capodichino), which is situated approximately 50km from Sorrento. You can hire a taxi, which you will find outside the airport, or you can hire a car and follow the directions that the car hire company will give you for Sorrento.
From the south, you need to arrive by FS (Ferrovia di Stato - State Train) to Salerno. From here you have options to get to Sorrento, which include by taxi, by SITA bus or by hydrofoil. From the north, you need to arrive again by FS to Napoli Centrale - Piazza Garibaldi. From here, again you have options for Sorrento. You can hire a taxi or you can take the local train line (Circumvesuviana) from Naples Centrale straight to Sorrento. You can also take a taxi from the station to the port of Mergellina and catch the hydrofoil from here to the port of Sorrento.