Hello, I am new to electronics. The engineers, who built circuits (their own), I want to understand how they know which resistor, capacitor, or other components they have to use in a circuit. And where do I learn all of this? To build circuits. I cannot ask this on the stack as it is subjective, so maybe you can help me.

@Momobear google, study, take notes, and google again

There was a "book/tutorial" written by electrical stack exchange people. Where can i find it?

first time i saw it was when i fist made an account here. But it didnt show up again since.

The Art of Electronics is a great reference book, as is Lessons in Electric Circuits. Do note, that "Engineers whom build their own circuits" can only do so after extensive education. If just a hobby, then approach it as such; however if you want to do this for a living, expect to devote the rest of your life to it.

I am pursuing robotics, so I will be head deep in it

@ChristianidisVasileios aaaahh I think you're talking about ultimateelectronicsbook.com