There are several ways of coming to Korčula, and you should choose the one best to your convenience.
The shortest way is by taking the highway to Split, and then take the ferry or catamaran for Korčula. The ferry and catamaran from Split dock at Vela Luka, where it is going to take you further 12km to Prigradica.
If you are not in such a hurry, you can take an old road through Plitvice, Gračac, Knin, Sinj and Šestanovac to the Makarska Riviera, and then take a ferry in Drvenik or Orebić. Ferries coming from Drvenik and Orebić dock at Korčula, which is another 45 km to Prigradica.
It is advisable to check the ferry schedule prior to your arrival.