More likely a solenoid problem. It's basically a big heavy duty switch. When you turn the key, and just get a click, that's the switch operating. If the engine doesn't turn it's either because the switch isn't conducting power to the starter motor, or the motor is seized.
Make it 'click' with your lights on. If they dim a wee bit, then the solenoid is not sending power to the starter. If they go very dim, then you are sending power to a seized motor - Don't hold the key in that position too long if this is the case.
If the starter is seized, try sticking the car in top gear, with the ignition OFF, and rock / push the car forwards and backwards a few feet.
If the problem is the solenoid, you can test this by shorting it out with a spanner - but I would strongly recommend that you don't if you are a complete numpty in this area as reported!!
Assuming that the lights don't dim mutch when you are 'on click' as it were, try repeatedly turning the key to the start position, so you get a click-click-click-click-etc. If it tries to turn on one of these clicks, then you definitely have a burnt out solenoid contact.
If it was me, I'd whip the starter out, strip the solenoid and clean the contacts - or replace them if they are bad (and if you can get spares). I have just done this on a 1999 Hilux, which has this as a weak point. Sounds like this may be the point when you need to reach for the phone and the credit card.
The good news is that Fiesta's tend to be simple (and cheap) to fix.
Good luck.
