The Fiesta has a hydraulically actuated clutch. The first thing that you should check is the brake fluid reservoir to make sure that you are not low on brake fluid. Both the clutch and brakes share the same reservoir. The reservoir is to the right of the battery. If the fluid level is fine, the seal on the clutch master cylinder is probably bad. When you push the clutch pedal in, the plunger on the master cylinder is supposed to force brake fluid into the slave cylinder, which pushes on the throwout bearing, which pushes on the fingers of the pressure plate, releasing the friction disc. This disengages the crankshaft from the input shaft of the transmission. If the seal on the clutch master cylinder is bad, it cannot create enough pressure to release the friction disc. If the fluid level is low, there are a couple of possibilities. One is the you have a leak at one of the brake cylinders or calipers. This will eventually cause the fluid level to be so low that you start introducing air into the line connecting the clutch master cylinder to the slave cylinder. The other possibility is that the seal on the slave cylinder is bad. This will cause brake fluid to leak from the slave cylinder. If the fluid level is low, you will need to put the car on jack stands or a lift to find the leak. At this point, you definitely do not want to drive the car until you find the source of your problem.