DS is the power exchange aspect of BDSM. It can (and frequently does) involve sex, but it doesn't have to. There is no specific activity associated with it. It is the dom/sub relationship itself. The surrendering of power from the submissive to the dominant over whatever the two have agreed upon; anything from what she will wear on a given day or what she will eat to punishment and sexual needs. Although, as TG says, the real power lies with the submissive as she will set the limits and call the safe word if things get to be too much. I hope this helps and don't be sorry for your ignorance, asking is the only way to learn sometimes.