You can only send messages to people you have connected with.
To send a message to a connection:
-
Click on the green bar on the right side of your screen that informs you of the number of connections you have.
-
The green bar will expand to show you the connections you can send messages to.
-
Click the name of the person you want to send a message to, and this will take you to the chat window.
-
Send a message!