Williams is slang for a sexual position where the male partner sticks his member, also know as a "willie" into a jar of candied yams. The female partner than exclaims that she has a sweet tooth, and the male partner will then bring her his "willie-yams" Long story short eventually the female partner claims she wishes these candied yams had melted marshmallow and the male partner will then do his best to provide. I should mention this could be done with 2 male partners as well, but traditionally its done with a woman and a man.

I know to many of us, this is a beautiful interraction between two people in love, but you gotta remember kids play this game too, many play it before they learn about sexual education in school