What is the job of a fuse?

A fuse is meant to blow (when the low melting point wire melts) to cut the power supply in the event of excess current, i.e. when a fault occurs. A type of fuse is altered depending on the appliance e.g. for a high power use, such as a kettle the number of amps allowed to flow through the wire is higher, obviously the wire is either thicker or made from a different metal in this case.