A button or menu choice on your mail program lets you check mail.  You must be connected to the Internet for your mail to be received from your ISP's server.  Typically your new mail arrives in an inbox.  To view a message, you simply click or double-click on it.  

Buttons or menu choices let you reply to the message or forward it on to another e-mail address.  Typically the original message will automatically be included in the reply.  You can highlight the portions you don't want to send back and press the Del key to remove it.  You may reply in line-by-line fashion to the original message (by clicking where you want your words to go and pressing Enter to start a new line) or delete everything and start afresh.  When you're finished, find the send button or menu item to send it on its way.  

Some mail programs put mail in an outbox when you click send.  If so, find the menu item that says Send Messages in Outbox (or similar) to actually deliver your messages.  

Composing Mail  
   
You may also initiate your own letter.  Find your program's control or new message button or menu item to begin.  

Typically there will be a To: field.  Here type the whole, perfect e-mail address of your recipient.  You can address the letter to several people at once; just put commas between addresses.  You can call up your address book to make addressing mail simpler.  

There may also be a CC: field for recipients of copies and a BCC: field for sending blind copies to others without the To: person being aware.  

It's courteous but not necessary to put a subject on your messages in the field provided.  

You can type your message as you wish in the space provided.  If you wish, you can also copy text from another window (switch  to the other window, highlight the text, press Control-C to copy it to memory) and paste it into the body of your message (click where you want the text inserted and press Control-V to paste).  

When finished composing your mail, just send as mentioned above.