For the random giveaway only, we use a Random Integer Generator.
The first thing I do is look at the total numbers of entries in the giveaway contest, for example i will take 500.
I enter the amount of prizes we have for the contest. For example, i will choose only 1 prize.
After this, i enter 2 for the beginning as I'm the first post, and I can't win and I enter the total number of entries, (501).
So now we're set up to generate 1 integer between 2 and 501.
Once i get that number i will find that post in the giveaways contest and i will give you your prize by Xbox Live Message !
I hope you understand now.