Email or electronic mail is a way to correspond, over the Internet, with friends, family and business associates around the world. The first part of the address is the username. This can be someone's real name or a nickname. Generally both parts are required for the email to get to the right location. Depending on the service, you may need only the username if you are sending mail to another person on the same mail server.
Email is about as private as a postcard.
It might be read on the way to or from you computer. Netiquette is etiquette on the Internet. It has a few conventions, just like etiquette, generally designed to help people get along. Treat others as you would be treated. Be ethical and lawful.