As Craig suggested above one of the best ways to learn about engineering disciplines is to do some research online. There youll find tons of videos and documents that specifically break down each engineering disciplines and it will paint a better picture so what things look like in the job force. Another great way to learn about engineering is looking at job listings. I know this might seem strange but not only will a job listing tell you exactly what you need to get the job it will also break down the job itself as a whole, the type of work youll be using and some of the tools that you will need to find success.
From the little that I have been exposed to mechanical engineering is a very broad area of study and while the degree focuses a lot of fluids and mechanical modeling the amount of avenues that the degree can take you down is quite large. For example a typical job title of a mechanical engineer is product development/ research and development. Both are very similar in the fact that your task is you solve the problems that you are given. Whether that be in aerospace, automotive, medical, manufacturing etc. There are always going to be advancements in technology and with that comes new challenges and new areas of product development.
Hopefully you find this helpful!