The Ford fiesta auto transmission is actually a newer, more efficient transmission design, called a Dual Clutch Transmission. It is actually an automated manual transmission that gets more miles per gallon out of your gas. It does have some noise during shifting, which are the little electric motors that push in and out the "mini" clutches in the gearbox. It is actually kind of cool - even if some don't like the difference in driving characteristics of this transmission.
Anyway, if you need transmission fluid - that would be a bad sign, maybe a leaking shaft seal. If you need to replace it, make sure you replace it with Motorcraft Dual Clutch Transmission Fluid XT-11-QDC. You normally have to get this through Ford. Sorry. Isn't cheap!! It is a special type of transmission fluid, kind of amber in color (if you have someone sell you something that is red, IT IS THE WRONG FLUID!)
Start with the vehicle in NEUTRAL, positioned on a hoist (you want the car as level as possible for the most accurate reading). You can also do this by lifting the vehicle on 4 jacks to keep it level, and high enough to take off the driver-side front wheel (makes this SO much easier).
Take off the driver side wheel. Locate the plug on the side of the transmission (see image).
CLEAN the are around the plug - you don't want dirt in that transmission!
Remove the fill plug using the correct sized Allen wrench. Righty tighty, Lefty loosely.
Using a oil suction gun/ Syringe Pump, fill the transmission (actually, the trans-axle) to the correct level. Add transmission fluid until the oil runs out of the fill hole. The trans-axle is full when the oil flow from the fill port has slowed to a broken stream or dripping. Do NOT overfill the trans-axle, this causes the fluid to be forced out of the case, which can damage your seals - not a good things, so make sure the car is level, and make sure you let the excess fluid drain out.
The picture below shows you what you are trying to achieve. Note that the green is the fluid (which is actually amber in color).
Re-install the fill plug. Tighten to 43 Nm (32 lb-ft). (You will need to use a ball head hex socket so that you can put on a torque wench).
Hope this helps!