I'm not trying to be a smart-**** but if you dont know where the reservoir is you probably ought to leave it alone.
I take it the brake warning light on the dash has lit up?
Please, take the car to a garage. If it needs topped up a lot there may be a leak in the system which could lead to brake failure.
If you really want to do such things yourself, ask at your local college about courses on Vehicle Maintenance, there are many run solely for women if you prefer. You will get a better understanding of your car and be (slightly) less likely to get ripped of by garages!!
gerrie mech., August 2009