r/PcBuildHelp or r/buildapc would be better spots for this

Either you buy all the parts and build it yourself, wich is just connecting them all together and screwing them into the case. Or you buy a prebuild one wich will cost a few bucks more.

Although building a PC is really not particularly difficult when it comes to actual assembly of it, it is not without its difficulties. It is not difficult for someone to give you a list of parts meeting your requirements that you can buy, and one of many detailed guides that exist for assembling one. The issue comes if something were to go wrong, and you are stuck with a computer that doesn’t work.
The hardest part is generally learning what you need to know to select, compare and find the parts that suit your need and that really needs a lot longer discussion than is useful here.

That being said, there is absolutely nothing inherently wrong with pre-build computers. Of course there are crap products around, but thats true for all kinds of products not just computers.
A lot of people just want a computer and rather spend their time using it than figuring out how to build one. You can get help in the previously mentioned subreddits for suggestions regarding reasonably priced pre-builts and that will do just fine.

If you wish to actually learn how to assemble and select parts all on your own, those subreddits would be useful for that too. But it is a skill and it takes a bit of time to learn. It also requires a lot of research and always come with the chance of failure which you then have to deal with on your own. This is generally the hardest part to learn, and potentially the most expensive.

It’s worth to remember that the overwhelming majority of computers sold across the globe, are pre-builts. We who build our own, are a niche of enthusiasts who enjoy it. And as enthusiasts, our requirements and needs do not generally match your average joe, if you will.

The best is always if you know someone who can help you out, a friend or the like. Or if you wish, local tech communities and groups may also be able assist sometimes. At least in my country we do that frequently and many of us are more than willing to give people a hand and share in our enjoyment of computers and tech in general. I have traveled across town many a times over the years to meet up with someone and help them build their first computer. You know have some pizza and a few beers, teach them how it works. Good fun. But of course, YMMV.

Here is a video that goes over how to build and what goes into it. It is a couple years old so is not useful for copying the build, but goes over the basics of how to build.