According to this theory, when surfaces of two bodies come in contact, then intermolecular force of attraction, also called force of adhesion, between the molecules of two surfaces comes in to play which tries to resist the relative motion between the bodies, This intermolecular force of attraction between the molecules of two surfaces in contact is the cause of friction. 

When the surfaces of two bodies come in contact, the actual microscopic area of contact is much less than the apparent macroscopic area of contact. Since the actual area of contact is very small, therefore, the pressures at contact points will be very large. Because of this large pressure, the contact points deform

plastically and many contact points actually become "cold-welded" together. The "cold -welding" between the molecules at the contact points creates a strong force of adhesion between the molecules of two surfaces in contact. When one body is pulled across the surface of another body, then a frictional opposition is associated with the breaking of these thousands of tiny cold-welding points.