If you are not sure what voltage an appliance is designed to run on, you should check the appliance's documentation before plugging it in.
In general, larger appliances, such as air conditioners, clothes dryers, and refrigerators, are designed to run on 220 volts. Smaller appliances, such as toasters, microwaves, and coffee makers, are typically designed to run on 110 volts.
If you have an appliance that is designed to run on 220 volts and you do not have a 220-volt outlet in your home, you may be able to have one installed by an electrician.