Circuit breakers are installed in a home's breaker box, with each individual breaker serving a different electrical circuit. The breaker's job is to either allow or stop power reaching the circuit. If there is a short or a power surge somewhere along the circuit, the corresponding breaker automatically switches off to help prevent electrical shock. However, the breaker also can be automatically turned off (tripped) by hand if the connected circuit needs to be worked on.
Plug a portable appliance into one of the outlets in the circuit that the breaker is serving. If working on a circuit with a previously installed appliance such as a clothes dryer or stove, turn on that appliance. Or, if working on a light circuit, turn on the light at the light switch.
Open the home's main breaker box front cover -- most breaker boxes have covers attached with hinges at one side or at the top. Look for the circuit breaker that powers the electrical circuit needing to be turned off -- many breaker boxes have a list of circuits with the corresponding breaker numbered on the inside of the front cover, so it is easily found.
Turn the switch on the front of the circuit breaker to the off position. Go back to the electrical circuit's location and see if the electrical appliance that was turned on is now off. If it is still on, the wrong circuit breaker has been tripped. Go back to the breaker box and turn off the correct breaker.