The diagram to the left, shows some of the main components and the basic configuration for this type of setup.
Basically, what happens here, is that you install a photovoltaic (PV) system at your house, which is connected to your household electrical system. However, you are also connected to the power grid through your electric meter. When your solar panels are generating more electricity than you need, it is fed back into the grid and it is like your electric meter is running backwards. At times when your solar panels are not generating enough power to meet your needs, then your meter is running forwards and you are using electricity from your electric provider.
This approach helps you reduce your monthly electric bill, but also provides you with the stability of always having the amount of electricity that you need, regardless of varying weather conditions that may affect the efficiency or electric output of your PV panels.