An instant message is a private message between you and another user. You can send this sort of message only to users who are connected to the server right now, and the messages are not recorded. Instant messages are private: They can only be seen by you and your interlocutor.

To open an instant messaging window with a user, click his nickname. In the menu shown, select "Contact", then "Instant messaging".

Instructions on how to use the chat panel are here.

You can block incoming private messages if you don't want to receive them. To do that, open the main menu. Press the settings button. Then select " Unsolicited messages > Instant messaging" in the main menu.

If you want to block messages from a particular user, ignore him. To ignore a user, click his nickname. In the menu shown, select "My lists", then "+ ignore".