How does the movement of electrons between two objects cause buildup of electric charges?

Electrons are negatively charged, they don't have to move to be that. If they do move in an otherwise electrically neutral material, they leave behind an imbalance in charge that is positive. The question is poorly Worded, possibly because of confusion, but in reality, nothing creates any charge, ever - charge is a fact of nature, it is always present and does not change. All that may change is the balance of positive and negative charges in any one spot.