As Wayne says, you have to be able to separate the the existing panel from the main entrance (existing panel) so that you don't backfeed to the utility. Anyone working on the utility lines is in peril.

Essentially, you feed a second panel (emergency panel) which feeds the things you want powered by the generator. When power is out, you disconnect the emergency panel from the existing panel. You also need to feed the emergency panel from the generator and, depending on proximity, just the wire and plugs can be rather expensive.

However, getting quotes only costs you time.