A part program is like a recipe for a machine that tells it what to do. Just like how you follow a recipe to bake a cake, a machine follows a part program to make a part. The program tells the machine what tools to use, how fast to move, and where to make cuts or holes. It's like giving the machine really specific and detailed instructions so it knows exactly what to do to make something. And just like how you can change a recipe to make different cakes, you can change the part program to make different parts on the machine too.