Although they work in different ways, fuses and circuit breakers broadly have the same purpose; to protect electrical appliances and electrical circuits from short circuits, and excessive current (called overcurrent or overload).
Fuses are relatively low cost electrical safety devices. If too much current enters the circuit, the fuse will burn out (sometimes called blowing out). When the fuse blows out it breaks the circuit. This protects the attached devices and allows you to touch devices without being electrocuted. When the fuse blows, it must be replaced before using the device or appliance again.
Circuit breakers work in a similar way to fuses, but they are resettable. Once a fault is detected (this is typically a short circuit or an excessive amount of current flowing through the circuit) the circuit breaker will interrupt the flow of current. When the circuit breaker trips, it's simply a case of flicking a switch to reset the circuit breaker. As soon as you've reset the circuit breaker, it is ready to use again.