Hmmm - RTFM I think.
STOP BEING SUCH A GIRL!
Your handbook will tell you where the coolant reservoir is. (The handbook is usually found in the glove box of the car - probably hidden under shiny things and CDs)
Open the bonnet (usually a handle to pull in on eof the foot wells somewhere to release the catch, then you need to feel around under the edge of the bonnet to find and release the safety catch. Lift bonnet. Remember to put the metal rod that holds the bonnet up in place)
Look for a plastic tank with dirty looking water in it. This is probably the coolant reservior. there will be a screw cap on the top.
Oh, and it's better to use coolant (mix of water and antifreeze) to top up, rather than plain water.
MrsMac, February 2011