Usually the fuse box is under the dash on the driver's side, although on some cars, especially foreign makes, it's in or near the glove box or in the engine compartment. Wherever, chances are it'll be hard to reach, another reason to carry a flashlight. Even on a bright day you need a flashlight to see the fuses on some cars.
Drive ove to your local service station and buy at least one replacement for each fuse in the box. Fuses cost 20-50 cents each; it's often cheaper to buy them at a gas station than a dealership.
How do you know what size to buy? Your owner's manual will tell you what size each fuse is. Also it's usually marked on the fuse box above or beside each fuse. And the letter markings are the length. You want to be sure that the replacement fuse in exactly the same as the fuse it's replacing. Carry the extra fuses and flashlight in your glove box. That way you'll be ready if trouble strikes.
Some fuses you can remove with your fingers. Others are harder to get a grip on. These you can pry out using a small knife blade, small screw driver, even a bobbypin. Or you can take a paper clip, bend it so there's a little hook on the end, place the hook around the fuse and pull it out. Main thing the remember, don't be ham-fisted. If you don't use a little dexterity, you can break the glass of the fuse you're trying to remove, and possibly the fuse next to it. [TEXT OMITTED FROM SOURCE]
To put in the new fuse, just push it back in the clips that held the old fuse. Be sure the one you put in is the same size as the one you removed.
When do you suspect a blown fuse? When something suddenly quits working. Say your radio, headlights, horn, brake lights. Often a failure in one of these is what causes the fuse to blow - from a resultant surge in current. If the fuse keeps blowing, however, you've got a problem that a mechanic should check out.
How do you check a fuse? Usually you can tell by looking at it. The filament will be burned in two, or the glass will be somkey. But sometimes you can't tell by looking. If the fuse looks okay, put in a new one anyway. If that doesn't solve the problem, then look elsewhere.