As a rule of thumb, utilities can be around 20% of rent if you live alone, and 10% if you live with others.
Electricity powers your lights, refrigerator, microwave, ceiling fan, and sometimes your oven, water heater, heater/AC, and all of your devices and appliances. This is a lot of stuff, which is why your electric bill can really get up there.
Gas is important for powering appliances like the stove, water heater, and heater in your home or apartment. Sometimes these appliances are powered by electric however, removing the need for gas altogether. It's also the most expensive utility.
Examples for each appliance on this site are directly from The West Edge, and are representative of the appliances there (except gas). Each location doesn't use the exact appliances shown of course, but these exist to give estimates, and can be helpful in determining which appliances are the most expensive, and how to better handle them.