New to Quake? Start here

What even is a source port anyway? A source port is a port of the source code for the Quake engine (originally only available for DOS platforms) to other platforms. Often times, these new source code ports will upgrade the capabilities of the game engine, granting mod developers the chance to expand the original game's content and compatibility to what was originally intended. In more general terms, a Source Port is just what us people in these retro game communities call a new engine derived from the original. Since the old engines no longer run on modern systems / weren't ported by the developers to consoles / etc, you'll need to have one of these bad boys to play Quake in all of it's glory on modern hardware. Right so I need a...
1What is this guide and who is it for? This guide is intended to provide people new to Quake custom content with a working understanding of how to install and run custom content of all types, as well as general setup of the game. There will be detailed instructions, but ideally anyone who has read this full guide will understand how things work well enough to not need step-by-step instructions every time they want to install things. This is not intended to replace documentation for each individual package, and I still recommend that you always read the readme. This guide should help in general in the absence of detailed instructions, and provide any knowledge assumed in vague instructions. It can also be helpful for creators to...