Source: https://openclipart.org/
Mechanical engineers do many different things, including some of the following:
Mechanical engineers work in a variety of fields such as car designs where they would look to make cars more effecient; developing heating and cooling systems for homes, chools, and even airplanes; or robotics where they build and maintain robots.
https://www.bls.gov/ooh/architecture-and-engineering/mechanical-engineers.htm