What is email?

Email is like digitally writing a letter to someone, accept it's free so you don't have to pay for postage and envelopes. I use my email when I need to send myself a document from a computer at school which I need for homework. I use it to sometimes communicate with family. I also you it so I know when stuff goes on sale at sporting goods stores. People in life use it to communicate with their co-workers or bosses, or friends and family. I don't think I know a whole lot about "email etiquette".