An inverter is an electrical appliance that converts Direct Current (DC) to Alternating Current (AC) or the opposite AC to DC. They are used in grid-tie systems to convert the solar panels DC power into AC mains or another example would be from batteries on a boat to provide AC power for electrical equipment onboard. Mobile system or off-grid inverters are either 12V, 24 V or 48 volts whereas grid-tied inverters are 48 volts.
Inverters can be broken into two installation categories which are either direct connected or integrated solution. Direct connect is when you attached the mains power plug directly into the inverters supplied AC socket. There is generally one of these on each inverter but some larger units have two sockets. The DC input should run through a fuse or circuit breaker and connect directly to the battery. The other installation variation is an integrated solution, it might include Auto AC switching which means when mains is turned on the DC battery power is no longer needed because the inverter has detected AC mains input and it bypasses the inverting function and supplies the mains directly to the AC output of the inverter.
The other variation with inverters which is also just as important is the sine wave generated. Mains power is pure sine so the best inverters are pure sine inverters. A cheaper alternative is modified sine wave but these units aren't good for many types of AC devices that could easily be attached to the inverters power sockets. Because the installer can't control what devices are connected it is safest to use only pure sine inverters. It's also better for any AC equipment attached.
Installation considerations are with integrated all your AC mains sockets can be used by either battery power or mains power. With direct connect you might need to unplug a device from the inverter and reconnect to a circuit that can only be used when connected to mains power while connected to shore or plinth power.