If you are talking about a portable electric generator, you plug your devices right into it and there would be severe limitations on how many you could run. You could use it to run a few electric tools during rehabbing but not in place of regular services if, say you want run the house. I bought one last year so I could plug in a sump pump and a couple lights or a space heater. Each generator is rated for the watts it can produce (including the start-up watts, which are higher) and it's amazing how your devices eat up that wattage when you have to pay attention to them.
Once my brother wired it so with a generator when the storm took out power that he.could run the whole house,He is handy with things,I Wouldn't recommend this.They do have to be outdoors because of fumes.
Nichol is right. I stand corrected. It IS possible (for an electrician) to install a power transfer system if your portable generator has a 30-amp outlet. It wouldn't run a household, but you could more conveniently run a few devices at a time.