To write a message to another user:

• hold the cursor over the picture of that user, wait for the pop-up window to appear, and select "Write message".
• You can also head over to your friend's main page and select "Write message" in the menu under his or her main picture.
• You can continue recent conversations with your friends by opening the "Messages" section and selecting the dialogue you're looking for.

Note that you are not permitted to send messages to users with closed profiles who are not in your list of friends. If you want to write a message to a user with a closed profile, first add him or her as a friend.