What is the difference between a circuit breaker and fuse

what are they both used for and how are they different?

They both are used to protect circuits from excessive current. They both will open the circuit when the current flowing in them exceeds a specified amount.

A fuse is a one-time thing. When the current exceeds the specified amount, a thin link of metal in the fuse overheats and melts, opening the connection. To restore the circuit to usefulness, you have to remove the burned out fuse, throw it away, and put in a new fuse.

A breaker uses the electromagnetic field generated by a coil of wire. When the current exceeds the specified amount, the magnetic field is strong enough to cause a switch to open, breaking the circuit. The mechanics are such that the switch is latched open, requiring human intervention to reset it.

Fuses have to be replaced when they blow. A circuit Breaker can be reset.