message to specific user

Some coding will be definitely required and there are many tiny details to consider depending on functionality.
Lets consider a simple example when admin sends messages to individual users. You are going to need a table to store message, target UserID, status (read/not read) etc. Admin has access to this table and can add new messages there. When user logs in you can run a SQL query pulling message or messages for the current user. If messages are found display them. This code snippet can be placed to header file.
Now you need to consider how long to display this message. For instance, you can change message status to 'read' right after it were displayed. Another option is to provide functionality for the end user to mark messages as read (this will be more coding intensive approach). You also need to remember to only pull messages that are 'not read'.

Thanks Sergey
Your responce is great, i will try to find solution by following your instructions. Most appreciated.