Please read the following pages from the U.S. Energy Information Administration.
Links
[1] https://www.eia.gov/energyexplained/index.cfm?page=electricity_home
[2] https://www.eia.gov/energyexplained/index.cfm?page=electricity_in_the_united_states
[3] https://www.eia.gov/energyexplained/index.cfm?page=electricity_delivery
[4] https://www.eia.gov/energyexplained/index.cfm?page=electricity_use
[5] https://www.eia.gov/energyexplained/index.cfm?page=electricity_factors_affecting_prices