You can use the Participants list in your LEO unit to select just a single user to send a message to. However, you may also use the Messages page in LEO to add a user as a Contact and send them a message.

How to add a messaging contact

1. In LEO, click your name at the top of the page. From the dropdown list, click the 'Messages' link:
   
2. On the Messages page, click the 'Contacts' button.
3. In the 'Search for a user or unit' box, type the name of the user you wish to contact. Their name should appear in the list under the search box:
   
4. Click the user's name to select them.
5. Type your message text into the chat box at the bottom of the messages panel, then click the 'Send' button:
   
6. You message text, and any replies, will appear in the Conversation window above the chat box.