How stress leads to strain?

How stress leads to strain?

The change per unit length or per unit volume of an object is called stain. Again internal restoring force acting perpendicularly per unit area of the body is called stress. Whenever an external force deforms a body, strain develops. Again, applied external force for developing certain amount of stain is equal to the internal restoring force generated on the body. Manly, this force acts against the intermolecular force of molecules of that object and causes strain.