You'll need to consult your owner's manual. This will show you the precise location of the fill plug/dipstick tube and provide instructions for checking and changing the transmission fluid. Trying to find it without the manual can be difficult and you risk damaging something.
Important note: If you're unsure how to check or change your transmission fluid, it's best to take your Taurus to a qualified mechanic. Incorrectly handling transmission fluid can cause significant damage to your vehicle.