Fuses are found in many locations, from the main consumer unit in your house to the plugs on most devices. Many electrical items, such as televisions and radios, also have fuses within them for further protection. A fuse is a thin piece of foil or wire, which vaporises quickly if an overload of current runs through it. This breaks the circuit and cuts off the power. To reinstate the circuit you have to replace the fuse.
Fuses are available in a variety of sizes and packages depending on the application. Fuses are rated by current. For example, a 13-amp fuse will fail if the current through it exceeds 13 amps. Some electrical items consume a higher current at switch on and so may be fitted with anti-surge fuses, which will withstand the higher current for a short period of time. Fuses are normally rated at just above the normal operating current to allow for tolerances and small surges. If a fuse fails you should investigate why before replacing it. If there appears to be no fault then replace the fuse with one of the same rating - do not use one of a higher rating as this will compromise safety. If the fuse fails repeatedly then there is a fault in the circuit, which should be investigated.