Overloading is when you try to draw more power from the inverter than it can handle. This can happen if you try to run too many appliances at once, or if you try to run an appliance that is too big for the inverter.
Overloading an inverter can cause it to stop working, but there is usually no damage if the inverter has built-in overload protection. After a few seconds, the inverter will try to start again automatically if the surplus loads are removed. If the inverter does not start again, it will switch off again.
So, if you think you might have overloaded your inverter, the first thing you should do is remove any surplus loads. Once the overload is gone, the inverter should be able to restart itself and continue running without any problems.