Can you get to Tarifa from Seville?

Here are a few choices from Rome2Rio.com. On the left of the screen just click on the icons for more info or the bars to expand additional choices.

Tgcomes.es.

There's bound to be an English icon somewhere on the site.

If not, the Spanish router box is pretty intuitive.

R2R has problems and should only be used for very crude preliminary planing when desperate.

rome2rio.com may be making me redundant
:-)
Presumably by now you have the detail.

That was because I'm on Dartmoor and your stupid British networks stutter. :)

Duplicate response has been deleted.

The good news, you can get anywhere in Spain by bus - cheaply and without advance reservations.

Every bus station I checked in Spain had an information desk or kiosk with an English speaker who can help you navigate your choices and book your tickets. Make sure you're clear on when and where to catch your bus, then come back 15 minutes prior to departure time.

I generally stop in the night before to book my ticket, just so I can plan my travel day. Buses may sell out in theory, but I've never experienced a sold-out bus (and certainly won't be sold out the night before).