Electricians can wire up and install electrical appliances for your house. They can install a new circuit board and wire your house to make it compliant with current electrical regulations. They can also install a RCD to make your house safer.
Yes, if you hire an electrician you should make sure that they are licensed and that it is current.
RCD stands for residual-current device. This is a device that is located inside your circuit board box and cuts the power to a circuit if it detects current leaking out of the circuit when it is not meant to be, this could be due to an electrical fault. If current is detected leaking it will trip the circuit out to prevent someone getting injured. RCDs have been required on all power circuits in Australia since 1991.
A circuit breaker is a device that trips if the level of current that the circuit breaker is designed for is exceeded. This could occur if you plug to many devices into the one circuit, circuit breakers can be reset by flipping the circuit breaker back on.
Yes, it is always advised to get a quote on how much a given set of work you would like done is going to cost you. A good electrician should be able to quote you for the work you want done and itemise what the work involves.