How are fuses and circuit breakers used to prevent circuit overload?

A fuse or circuit breakers are used to prevent oerload of a curcuit by the fact that they have a trip in them wich will open the curcuit if it is tripped preventing a curcuit overload in the system it will cut off the power to any wires wired to that curcuit.
if the circuit overloads the amp rating of the breaker it trips thats why it is important not to oversize breakers because if circuit is overloaded it will cause damage to wire