At some point during a vehicle's life, a fuse will blow. These fuses are meant to blow so as to prevent an overflow of electricity that could possibly cause a fire or other damage. If your vehicle has any sort of electrical problem, such as the interior lights or radio not working, the first thing you should check are the fuses.
Find the Fuse Panel
The owners manual that came with your vehicle will contain the location of the fuse panel. Typically it is located in between the steering wheel and the driver side door. There will be a panel covering the fuses that matches your vehicle's trim, but is removable. Remove the panel, and the fuses should be visible underneath.
Once the fuse panel cover is removed, the backside of the cover will have a fuse diagram which explains which fuses relate to what systems.
Find and Remove the Blown Fuse
There will probably be a dozen or so fuses to look at. Finding the blown one is essential. You can use the fuse diagram to locate the likely location of the fuse (eg: if the radio isn't working - locate the fuses that deal with the radio), or you can simply search by eye for the blown fuse.
The blown fuse will have a broken metal filament inside (breaking the 'flow' of metal), or possibly will look black.
Replace the Fuse
Once the blown fuse has been discovered and removed, a new fuse must be inserted. This fuse should be the same amperage as the previous one. If you are unsure as to what amperage the fuse is, consult the owners manual or fuse diagram.
If you do not have a spare fuse to use, you can 'steal' a same amperage fuse from a less critical system - such as the cigarette lighter or radio.
Verify that Everything is Working
Once the new fuse has been inserted, replace the fuse panel, and power up your vehicle to ensure everything is working properly. Most electrical problems in a vehicle can be solved by simply changing the fuse. However, if the problem is still present despite having a new fuse, check to make sure the new fuse has not also blown and book an appointment with your local mechanic to get things fixed.