Many of us bought pre-assembled PCs for flight simulation from brand-names, like HP, Dell. I did the same until one day I stepped forward to build one myself.
Frankly speaking, the first time was scary. Fortunately, I had done a lot of preparations; the work turned out to be far less difficult than anticipated.
Above is “A Complete How To PC Building Guide for Beginners” from MSI, which I found universally good. Definitely worth a favorite entry in your browser.