Use this site to get an idea of the core components of a desktop and possible costs
If you dont know anything about a pc, id recommend that you just play around with it for a while and make "mock" builds.
I normally recommend starting with their desired appearance (the outer case) and budget, and then work from there, as it narrows down the hardware choices far more efficiently than asking someone what they intend to use a computer for, only to be met with a boilerplate response of "email and youtube". It sounds counterintuitve, but I find that people are more engaged with building a pc when they have a clear vision of the pc itself i.e. aesthetics and follow through rather than getting stuck on chipset form factors.