Electricians are able to wire up a new house or repair or change the wiring in your old house. They can add a new circuit when needed and add safety switches to your power circuits.
Yes, to be able to practice as an electrician you are required to be licensed in the state in which you work.
This may be due to overloading the circuit or it could be due to an electrical fault. If you have very few appliances plugged in and it keep tripping out then you may wish to contact and electrician to come out and diagnose the problem.