Giveaway Help

I have been asked by a company to receive a software program on Memories....sounds great....I get two of them...one to keep, use and review...the other to give away.....I am deciding to do this...but...while I have entered many a giveaway....I have never run one....









           

So what I need is some help as to go about doing this.  Can anyone point me in the right direction? or explain what it involves.....how do I pick the winner?