How can you assemble a desktop on your own?

https :// www . wikihow . com / Build-a-Computer

I believe that researching the components, how they relate to what your consumption requirements are, and to no small extent understanding what your needs actually are, is the most important part of the process. And even with all that research, you'd have to see some things in action to get a feel for how well they perform.
The assembly itself is prolly not as great a challenge as you expect. Parts are made to a quasi standardised spec, so it falls short of the kind of mechanical aptitude & education required for complex machinery or custom innovations.
As a programmer and gamer, I was fine for many years sticking to generic purchases and tangential awareness of the hardware beyond ad hoc software repair & management knowledge. A lot of the industry feels like utter hype, where in a few years the bleeding edge becomes old hat (see moore's law).