The USA has two main types of plugs.
A 30 amp plug that supplies one hot, one neutral, and one ground wire and is 110 volt only.
A 50 amp plug supplies one ground, one neutral, and TWO hot wires. The hot wires are each 110 volts relative to the neutral, and are 180 degrees out of phase, so are 220 volts relative to each other.
Note that people talk about voltages of 110, 115 and 120, but they are all (for all practical purposes) the same. Same with 220, 230, and 240.