Welcome Maat_Mons.
I second what Jo says above. Building things teaches you a lot more than designing and thinking about things. Even playing with things teaches you a lot.
I humbly suggest: Acquire a pre-machined engine kit and put it together, look for areas of improvement and make it better. Or get a 3-D printer up and running to check your theories about things. Or, search the web for "engines" made of wood, legos, or other things. There are also "finger engines" where you press a lever or turn a wheel to demonstrate the motion of the engine or other device.
I avoided getting into machining too long while I waited for the money, space, and time to buy professional full-sized machines . I finally got a Mini-Lathe and starting for myself with smaller ideas. It's also more fun to take a project somewhere in a shoe box to show friends and family what I do.
ShopShoe