The 'hold' command can be used in two different ways. First and most common, it is used to hold something in your hand, i.e. 'hold <thing>'. You'll need to do this to use many items, like weapons. To stop holding something, use 'remove <thing>'. The second way to use 'hold' is to grapple someone and prevent their movement. To do this, simply 'hold <person>'. Your Strength rating, versus your opponent's, will determine your success and how long the hold lasts.