The virtual console is software that runs retro games on your wii, each game can be downloaded from the wii shop channel for wii points. Wii points can be bought from game shops etc.
Once you download a virtual console game, the game will be displayed as a channel on your wii menu screen, you can just click on the channel and click start to play.
Note - You need a classic controller to play virtual console titles unless otherwise stated before you download.
Hope this helps,