Best way to travel from Seville, Spain to the Tarifa ferry
First, you probably figured out there is no train service to Tarifa. That leaves the bus, Comes ( https://www.tgcomes.es/ ) runs the route direct (I believe it is direct), takes just over 3 hours, several buses a day. The bus leaves from Sevilla Prado station.
Be aware, the bus station is over 1 km from the ferry.