Instructions
Plug the controller input on your PS2 multitap into the "Controller 1" input on the front of your PS2 Slim.
Connect any controllers that you want to use with the multitap to the controller inputs located on the multitap itself.
Turn on your PS2 Slim. The multitap will allow all controllers to be recognized by the system, which will allow you to play with up to four players in games that support this level of multiplayer functionality.