Go to 'MyMessages' in the top bar with the dark brown background. When you hover over it or click a dropdown will appear saying "Read your messages""Send a message".
If you click on "Send a message" a form will appear. Copy and paste the contact you wish to send the message to into the "To" box. There is a Subject box below and then a text area to type into.
You can then Send, Preview or Spellcheck A pre-ticked box if you wish to save a copy.