
Short for electronic mail, e-mail or email is text messages that may contain files, images, or other attachments sent through a network to a specified individual or group of individuals. The first e-mail was sent by Ray Tomlinson in 1971. By 1996, more electronic mail was being sent than postal mail.
How to send and receive e-mail
To send and receive e-mail messages you can use an e-mail program, also known as an e-mail client such as Microsoft Outlook or Mozilla Thunderbird. When using an e-mail client you must have a server that stores and delivers your e-mail this service is provided by your ISP but can also be a service provided by another company. The e-mail client will connect to the server to download all new e-mail and deliver any unsent e-mail.
An alternative way of sending and receiving e-mail and a more popular solution for most people is an online e-mail service or webmail such as Hotmail, Gmail, and Yahoo Mail. Many of the online e-mail services including the above examples are free or have a free account option.

Writing an e-mail
When writing a new e-mail message a window similar to the example below will appear. As can be seen, several fields are required when sending an e-mail, the From or Reply-To is a field that is automatically filled out and is where the e-mail will return if a reply is made. Next, the CC or Carbon Copy field allows you to send a copy of the message to another e-mail address, but is not a required field. The To field is where you type the e-mail address of who you are sending the e-mail address. Next, the subject line although not required should be a few words describing what the e-mail is about. Finally, the message body will be the location you type your message and is what will contain your signature.
Source: http://www.computerhope.com/