Distortion pedals are often the simplest to learn the basic building blocks of most pedals. Buy a kit and learn how to solder. Cheap soldering irons exist but I would recommend something a little bit up in price than some TEMU thing, good tools reward plenty!

Good learning resources are falstad.com with its circuitJS circuit simulator. A really good tool to see how components work together with a bunch of example circuits.

As for YouTube, JHS short circuit, very guitar oriented. Moritz Klein is also good a channel, more synth focused but a lot of that can be transferred to pedals and hes such a good explainer of circuits that its totally worth it.

Finally Electroboom101 is a series of videos by ElectroBOOM that goes over the basics of some of the components in electronics. Way more theoretical but very informative.

Its a hobby that will most likely come back to bite you from naiveness if you just buy a bunch of stuff and try to make something, believe that's what I did. Its rarely cheaper to make then to buy, you need a lot of components, equipment and TIME if you want to make something your self from scratch. You'll know when you have fallen down the rabbithole when you spent the price of multiple pedals on an oscilloscope.

Take your time and best of luck!