Glycemic load is a calculated value. It is fairly confusing but here goes:
Glycemic Load = Glycemic Index * (grams of absorbable carbohydrate/100)
Thus if a food has a glycemic index of 100 and you obtain 30 grams of carbohydrate from eating it, the glycemic load is therefore 30. The problem is that now you have know not only a food's glycemic index but it's carbohydrate content. It grows rather tedious.
The benefit of knowing the glycemic load of a food is that it takes account of amount and therefore more accurately predicts a food's effect upon blood sugar over time.