Use it whenever you need electricity if a plug-in isn't available.
Two times that we often use ours is like when we pull off the road for lunch and need the microwave and may want the A/C on while eating.
Or, since we have a rear end diesel pusher, if we're going to go to sleep shortly after arriving someplace when it's nwarm outside we'll start the generator and air to cool off the bedroom over the engine.
Since you're new at this, if you have a gas generator, it will stop running when the fuelmtank gets down to about one third full.
Bill