I’m building my first PC but I don’t know how to plug in certain cables

Hey. I just started my journey building my first PC. The reason is I’ve always found it really expensive to buy a prebuilt PC, so I’m going to start building my own. Buying part by part: graphics card, RAM, motherboard, NVMe SSD… basically, everything.

Before all that, I already started learning the basics of cable management, because I think that’s the most important part of all. It’s really sad to have a beautiful setup with that mess of cables all over the place.

Anyway, I’m at the final stage of the build now, but I don’t know how to plug in the tiny case wires. The LED one, the beep one, and the power button one. My motherboard is from Asus and it has a diagram for the connectors, but it doesn’t really make much sense to me. Some headers have more holes than they should, and I’m terrified of frying something because of positive/negative.

Another thing I didn’t understand is how to connect the power supply. I finished installing it, but there are still a lot of cables left that don’t plug into my motherboard. Other than that, I already connected it to the graphics card. But now I’m lost about what to do with the rest.

If someone could be kind enough to help me out or send a tutorial made for dummies, I’d really appreciate it.