When you are creating a new message, you will be presented with a blank form. The available fields are To, Subject, and Body.

First, select a user from the To drop-down list. The available users will depend on your access permissions.

Once you have selected a user to send the message to, go ahead and fill out the subject and body of the message.

If you decide that you do not want to send this message, click the Discard button at the top of the page. Otherwise, click Send to send the message. This message will now appear under your Sent Items in the Message List view.