It can't be used, for example, to run an air conditioner. A generator is another source of electric power. It's probably going to be powerful enough to operate your air conditioner. A good tip is to make sure you turn on the generator for an hour or more at least once a month. If you haven't missed it, you probably don't need it.
Generators usually come equipped with an hour meter.
If you buy a used unit and see very little time on the generator, you'd probably want to check to make sure the generator doesn't have leaking seals from disuse. And if you're out in the woods, you'll be using your 12 volt water pump. When you turn on a faucet, the water will flow, and the water pump will come on again to replenish the water pressure. Going down the road is like a 3.5 earthquake, so turn it off. Breaks or leaks can occur, so turn the water pump off when you're driving.