Obtaining, Designing high quality Sound and Visual Assets

Greetings, everybody. I’m curious to know how someone like me, a singular person, would be able to obtain or even create and design good and quality sound and visual assets. Here’s a few examples of what I mean.

GAME: Runker 51

GAME: The Electric State DarkRP

That’s what I mean by visual asset. Now, I can’t record sounds on my computer, so I don’t have any examples of audio assets. But games like the aforementioned Electric State DarkRP have great sound that I admire.

Anyone with experience in these regions of development, tell me where I could acquire these kinds of assets, or even better, make them myself?