I suggest that you start with just printing the name when the player is put into the server. Get that working first using client_putinserver(). Then, you can add to printing only to admins by replacing your client_print() with a for loop that goes through all connected players and then calling client_print() only on those that have admin access. I suggest that you look for other plugins and threads where you see get_players() being used, most of these will have an example of how to use it and its results in a for loop.