An inverter is an electric apparatus that changes direct current (DC) to alternating current (AC). It is not the same thing as an alternator, which converts mechanical energy (e.g. movement) into alternating current.
Direct current is created by devices such as batteries and solar panels. When connected, an inverter allows these devices to provide electric power for small household devices. The inverter does this through a complex process of electrical adjustment. From this process, AC electric power is produced. This form of electricity can be used to power an electric light, a microwave oven, or some other electric machine.