A Mechanical engineer is a person who applies the principles of engineering, physics, and material science for the design, analysis, manufacturing, and maintenance of mechanical systems. A Mechanic is a tradesman, craftsman, or technician who uses tools to build or repair machinery.

A mechanical engineer can develop and plan a machine without any previous machine of that kind. A mechanic will always perform some task on a machine developed by engineers.

Mechanical Engineer uses the knowledge and he knows why the machine works and he knows how the machine works. He designs machines. He manufactures machines. Mechanic repairs the machine.

sources: https://www.quora.com/Whats-the-difference-between-a-Mechanic-and-a-Mechanical-Engineer