Physically putting together a PC is actually pretty easy. About like putting together some furniture you got at Ikea or something. IMO the harder/more time-consuming part is on the software side: getting the OS installed, getting all the drivers set up, and getting all your other crap installed & running. It's a good idea to download all the latest drivers for your hardware to a USB drive before you begin, BTW.
I'm gonna disagree with those who say you'll save money by building your own. That was true years ago, but these days, price competition has driven things down to the point that buying a system on sale at Best Buy or whatever will probably be at least as cheap and a hell of a lot quicker (time is money, yo). To me, it's more about getting the exact parts that you want.
Think about how
large of a system you need. This is another place where prebuilt systems usually win: all their parts are custom-made, so it's easier for them to be made smaller. Mostly, this will come down to how many PCI-e card slots you need. These days, a lot of stuff that used to be placed in expansion cards is either built into the motherboard or connected via USB. Most people don't need a full-size ATX tower, micro-ATX is plenty, and mini-ITX is perfectly viable for even some fairly high-end builds as long as you double-check the video card's dimensions.
Next question: do you need a dedicated video card, or is integrated video enough for your needs? If you're not a heavy gamer and aren't doing 3D modeling or anything, integrated is fine. Get an AMD Ryzen if you're going with integrated video. Intel says their upcoming Xe stuff will be better on the video side, but I'll believe it when I see it. And right now, I'd mostly recommend AMD over Intel on the CPU side - they're just a better value overall.
I would skip PassMark's benchmarks (CPUBenchmark.net linked above) - they're not exactly a real-world test. If you want to get into the nitty gritty, you could dig into
Anandtech's Bench, but honestly, you might as well just skip to the bottom line and check out their Best ____ Guides (menu at top-right).
From there, you could maybe look over PC Part Picker for some build ideas. When you're ready to start buying,
Newegg is the most popular place to get parts, but do some price comparisons on Amazon and such, too. Just browsing Newegg can give you a lot of alternatives for things like video card and case. Like you might find a build guide you want to use that has an ASRock RX-5500 video card, but then when you browse Newegg you might find a similar RX-5500 card made by Sapphire for cheaper than the ASRock card - might as well save some money. Newegg also has a really good search feature, like you can search by max GPU length if you're doing a small case build.