Getting to Formentera is quite easy, as you can catch a boat from the Spanish mainland with your car from either Barcelona, Valencia or Denia to Ibiza Eivissa and from there catch another ferry to Formentera. In the summer months there are direct ferries between Denia and Formentera. Alternatively, you can fly to Ibiza and Formentera can be reached by regular ferries from the Estacion Maritima in Ibiza Town and by tourist ferries from other parts of Ibiza during high season. The boat from Ibiza Eivissa to Formentera takes around half an hour, and leaves every half hour in the summer. The boat trip costs between 17 and 24 euros per person for a single trip. You can buy the ticket on the boat, and you do not need to reserve, but if you want to take a car it is best to reserve during the high season.
Next to the standard ferry there is a yellow speedboat ferry for around 30 euro per person for a return trip. The speedboat starts from the beach of Platja d'en Bossa near Figueretes.