Not too much to add to what's been said. If building your own, the biggest thing is to ensure the graphics card, ram, and cpu are all compatible with the motherboard you choose. If you use pcpartpicker, it should help ensure all chosen parts are compatible. You can also view their pre-designed builds at
https://pcpartpicker.com/guide/.
You can also go to newegg.com, search for the component (graphics card, cpu, etc), select up to 5, and do
side-by-side comparisons (selected some random ones just for the example).
Make sure you're grounded when handling the components. You can get these little wrist straps for around $8 that work really well (
Amazon link). You just strap it to your wrist and clip the other end to a metal component (like the computer case) and your components should be protected from your static electricity.
Overall, it can be a very stressful endeavor, considering the cost of the components, but it's very rewarding when you finish the build, flip the power switch, and see the computer turn on. But when you flip that switch and nothing happens, it's like the loudest silence ever lol.
[edit] One final thought is about storage. You'll certainly want your main drive (the one containing Windows) to be an SSD. It's tough to beat the
Samsung Evo. You could get away with the 256gb for this drive and be totally fine, but you would certainly want more storage. Depending on your budget, you can save some cash by going with a hard-drive for file storage. This way, Windows is still on an SSD and will be lightning fast, and you can still have terrabytes of storage space for very little cash.
So, you could do a single large (500gb+) ssd that holds windows and everything else. You could do a small ssd for Windows and a giant hard drive for inexpensive file storage. Or, you could do the small ssd for Windows, and a 2nd ssd for more performant file storage.
Since this build is for gaming (and since it's 2021), I recommend doing the 2 ssd's if your budget can support it; one for Windows and one for your game library. You can get away with a small amount of storage if you're ok deleting old games to make room for new games.