Ray is the man for this, but your domestic stuff, fridge, aircon, microwave, hot water heater (if it has an electrical one) and battery charger are all probably the original American 110v ones. An aftermarket transformer will have been fitted as Ray says to reduce your UK 220/240 volts down to suit.
When unplugged from the mains the generator (if an original fitting) will be 110volt and will run these as it should.
Be very careful not to run the generator when you're plugged in to the mains.
Is there also a built in inverter for running the sockets from the battery?
I need to switch manually to bring my inverter in, but al the rest is automatic.
More information as Ray says. Maybe a few photos of anything you don't understand, Alan.