The distribution lines are higher voltage - roughly 4800v. This is dropped down to 220/240v to supply anywhere from 1 to a series of homes. The 220v/240v is usually brought into the home using a 3 wire lead. 2 power/ 1 neutral. Power to power is 220v/240v. Either power lead to neutral is 110v/120v. Ground is commonly supplied on-site by an earth ground rod or water pipe ground connection. The 220v/240v is used for high current loads like cooking ranges, electric water heaters, electric clothes dryers, electric home heating, etc. Lighting and wall outlets are supplied with 110v/120v. The idea was that this lower voltage is safer for consumer contact use than 220v/240v. So where you are used to 220v/240v wall outlets, we typically only have 110v/120v outlets. Technically if someone wanted to they could in fact wire their home for 220v/240v outlets if they wanted to as they are supplied with that voltage by the electric utility.