how to hook laptop up to amp and sub

hey i have an old sony amp and a rockford fosgate sub , i was wondering how i could hook this up to my laptop, my buddy at my old job did this to his laptop at work i just cant remember how he did it,

If the amp has a hi level input to it, just hook it up to the headphone jack. If it doesn't, hook it up to the headphone jack anyways....but beware...if you turn it up too loud, you may distart\blow the sub

Im just curious as to what your trying to accomplish? Whats the need for the computer?