It will be better if you read about PLM, at least in wikipedia. PLM includes making the product. Some machines use CAM softwares (another PLM Solutions) to manufacture parts. Sometimes the skilled workers work on the parts based on the print out made by the designer. it varies amongst industries.
Between designing there is a testing phase. (another stage of PLM). Yes, prototype is indeed expensive. Testing is done with CAE software as much as possible to lower the dependency and cost of prototyping.
Therefore you have Engineers doing stuffs like designing, testing and finally manufacturing.
anyways, it is better to do a research, as least on wikipedia or google before you ask impatiently. There are certain basic stuff with answers available easily on internet.