Fuses play an important role in protecting your car's electrical components from potentially catastrophic damage -- damage that could spark a fire and pose a serious risk to your safety and the safety of your passengers.
Fuses are "rated" for a specific amount of current. If the current exceeds this amount, it blows; thus, preventing the current from traveling to the connected electrical component. Blown fuses are both good and bad. They are good in the sense that it worked: it protected your electrical component from current overload. But it's also bad in the sense that it indicates an underlying problem, such as a shorted wire. In any case, you should refer to the following steps below to test your car's fuses.
When you are ready, go ahead and pop your hood and look for the fuse book. Most cars have one or two fuse boxes, typically located near the battery or engine. With the engine off, disconnect the battery and remove the pull out the fuses. There are several ways to check fuses, including both a visual inspection and a more accurate test using a multimeter.
For a visual inspection, look to see if the if the fuse is intact. A "good" fuse should have a solid center, without any breakage or openings. If there's a break in the middle of the fuse, it's probably blown, in which case current won't pass through it. Visual inspections aren't 100% accurate, however, which is why it's a good idea to use a multimeter.
Multimeters work by measuring AC and DC voltage, resistance and the flow of current. When testing a fuse, you can use it as an ohmeter or ammeter. Simply connect the positive lead to one end of the fuse and the negative lead to the other. Assuming your multimeter is set to either an ohmeter or ammeter, it should transmit a small but noticeable amount of electricity to the fuse. If the current passes through, the multimeter typically makes a buzzing sound, indicating that the fuse is still good. If the current doesn't pass through, it won't make this noise, indicating the fuse is blown.
Of course, it's recommended that you replace any blown fuses with new fuses of the same current rating. Until those blown fuses are replaced, the connected electrical components simply won't work. Hopefully, this gives you a better understanding of car fuses and how they work.