Electronic mail, or email, allows users to compose messages on one computer that can be read on another computer when the recipient logs in. Key etiquette points for emails include using the "To:" and "Cc:" fields appropriately, writing clear and concise subject lines, proofreading for spelling and grammar mistakes, using appropriate language without abbreviations or emoticons, and structuring emails with shorter paragraphs and sentences for readability. Proper email etiquette helps ensure messages are effective and professional.