It's like sculpture: 'Carving' is a method of subtraction-taking unwanted portions and cutting them away. 'Molding' is a method of addition, slowly adding and shaping to the form you have in mind.
就像雕塑，『雕』是減法，把不要的部分去掉；『塑』是加法，慢慢堆積捏塑出心中想要的造型。