Usually starts with "this can't be THAT hard to add this to my project, let's try it". Six months later you've got a solid working knowledge of running a lathe and you've started teaching workshops to other hackerspace folk on how to run it because everyone has seen you running that machine and needs help on it. Then you realize you forgot to finish the project that sent you down this road in the first place. You get bored and stop using the lathe for a few months. "Hey, it can't be that hard to design a PCB for this project, lets do some of that now..." Six months later you're teaching workshops on it...
And then years down the road you know how to make most things from scratch from the electronics design, PCB gerbers, and the enclosure both in metal (both machined and fabricated), laser cut, and 3D printed. But just conjuring up any cool thing you want to make summons a mental spreadsheet of the time it will take to complete the project, possibly including making a small-run of extras to sell for much less than your time is worth, and then you set your drink back down and shake your head because ain't no one got time for that any more. And then you buy the Etsy/Kickstarter version instead because you realize they have woefully underpriced their super cool widget.
You don't need a certification that attests your knowledge on the labor market when you are doing something as a hobby. I know it sounds weird, but you can just do it and fail and repeat until you can.
The hardest part by far is figuring out what you want to do. Even if you think you want to do a hundred different things and you can't do them all, you still have to figure out what you want to do.
With KiCAD and dirt-cheap PCB manufacturing, the PCB design is just a matter of starting with something simple. It took me a (long) evening to go from nothing to an VGA I2C Atari joystick controller board. [1]
Once you've got the hang of it, more complex PCBs aren't really that much different.
I started with double-sized PCBs, but 4-layer PCBs are now almost equally cheap, which makes routing a lot easier too.
Lots of entry points, but the best way is to just start a project that’s simple and learn as you go. Electronics have gotten pretty accessible with arduinos, rpi, circuitpython boards etc. machining does take shop time to learn. Friends, maker spaces, school shops, all are options but that’s hard. Sometimes you don’t need much to get going.
And then years down the road you know how to make most things from scratch from the electronics design, PCB gerbers, and the enclosure both in metal (both machined and fabricated), laser cut, and 3D printed. But just conjuring up any cool thing you want to make summons a mental spreadsheet of the time it will take to complete the project, possibly including making a small-run of extras to sell for much less than your time is worth, and then you set your drink back down and shake your head because ain't no one got time for that any more. And then you buy the Etsy/Kickstarter version instead because you realize they have woefully underpriced their super cool widget.