To compose a new message, click the New link at the top of the Inbox list. To reply to a message, click the Reply icon, an envelope with a purple arrow pointing left - or click the Actions link at the top of the message window and select Reply.
A new window will open where you can address and compose your message. If you need to save your message for later, use the Save (disk) icon at the top of the window. The message will go to your Drafts folder (accessible from the navigation bar), where you can go back to it later.
If you wish to include one or more attached files in your message, click the Attach File (paperclip) icon.
To immediately send your message, use the Send button.
For more information, see Microsoft's Create a Message help.