Is there any mechanical engineers? What you would wish to know when you were starting learning? What skills and topics you consider the most useful in mechanical engineering?
What is the fastest way to learn mechanical engineering in the nowadays when 3d printers are avaliable to be able to design and make custom clocks, engines, generators?
There's no quick way to learn Mechanical Engineering. The field is extraordinarily broad. Hell, the degree merely gives you an overview of each branch, and you'll wind up having to learn so much more beyond that. Learning design is a good way to learn how to apply engineering practices and rigors, but the application of actual engineering principles is a never ending learning opportunity. There will always be a better way to do something: a cheaper way, a faster way, a lower energy way, a safer way, or even a combination of several of these.
It's like anything else. It takes practice and a good understanding that you don't know everything....and that's perfectly okay.