How did the second battle of El Alamein contribute to the Allies victory in World War 2?

It wasn't one of those battles involving vast numbers of men. The significance of El Alamein in October 1942 was that it meant (in the context of the time) that the Germans would not reach Cairo and would not take the Suez Canal or disrupt British communications with India and the Persian Gulf. Moreover, from that point on the Axis was on the retreat in North Africa.