The receptacles, light fixtures, appliances and switches in your home are all part of multiple electrical circuits, which begin and end in your circuit breaker panel. For example, all the receptacles in a bedroom might be part of one circuit, wired to a single breaker.
For simple additions, such as installing an extra receptacle, you may be able to extend an existing circuit. As long as adding the load doesn’t exceed the circuit breaker’s amperage rating, you can splice wires leading to the new receptacle to the circuit’s existing wire. But if you’re wiring a new room or installing a high-wattage device like a major appliance, you need to add at least one new circuit, with its own circuit breaker in the breaker panel.
Always consult local building wiring authorities before working on your household electrical circuit. New circuit wiring must meet local electrical code standards, and you may need to acquire a permit. Additionally, both your plan and the finished work may need to pass an official inspection, and local authorities may require that a professional electrician handle certain parts of the job.