Take a look at the cars handbook, which should list the fuse numbers, together with the items that are protected by each fuse. If other items are listed along with the brake light fuse, check to see that these electrical devices function OK. If not, it is highly likely that the fuse has blown.
Option 1, take your car to your local garage to fix it; to be honest it should not cost more than �30 for them to fix such a simple problem. Agree a price before allowing them at your car, otherwise they might decide you need a new battery and alternator, and they need �300.
Option 2, With the cars ignition on � remove the two connections from the brake switch, use a piece of bare wire, link the wires together, if the brake lights are on, then the brake switch is faulty. Using a multimeter (buy a cheap one for less than �10), measure the voltage from the make shift link (shorting out the brake switch) to the vehicle chassis. If this voltage is 0V, then there is a break in the 12V supply to the brake switch (check the fuses again). If it is 12V, remove the one of the brake light bulbs, and measure the voltage from the centre bulb contact to the chassis. If it is 12V, then either the bulb has blown, or the wire link from the brake light to the chassis is broken (or has a poor connection). If the voltage at the bulb contact is 0V, there is a break in the wiring between the brake switch and light. Remember that the vehicle ignition must be on while making the above measurements.