The circuit breaker works with a bimetallic strip inside of it that heats up when current passes through it. When the current exceeds the current rating of the breaker, it will cause the breaker to trip. Most tripped breakers will put the switch between on and off so that you can tell it was tripped. To turn it back on you need to set it to off and then back to on.

While circuit breakers are good, there's some things you should know. Since every time the breaker trips there's some arcing, eventually the breaker will wear out and stop working. Also, since it's depending on the bimetallic strip to heat up, many times the rated current of the circuit could pass through it for a brief period of time, which may cause problems with equipment powered on that circuit. This is why you still need surge protection or power conditioning.