A generator is a device powered by Gasoline, Diesel, Natural Gas, or LP Gas, that will provide electricity to your home. Generators can be portable or stationary and that will depend on the space you have for the generator.
Gasoline models are the least expensive to buy, but have short run times and will need to be filled 
often. In our recent widespread power outage, gasoline was hard to find, due to many of the stations not having electricity to pump the gasoline. So you may need to consider this in your purchase.
We also found this to be a problem with LP Gas. There was such a run on LP Gas for portable heaters & generators that a lot of the local providers did not have enough to supply the demand. You should be willing to put a large LP Gas tank in your yard if you consider this as an option for your generator.
The generators that can be hooked up to natural gas can provide continuous power since they are hooked up to an external fuel source. They to have their drawbacks, depending on the disaster. An earthquake could rupture gas lines, leaving no fuel to supply your generator.
Do your research and talk to a qualified electrician to determine your needs and how they can be met. Be safe.