I know the Series X is the main console and is far more powerful than the S but what is the difference? How much more powerful is it?
There are lots of comparisons out there what will go into the fine details of giving you numbers in teraflops and stuff, but these values are fairly useless for most people.
This post covers the differences between the two consoles in a simple way that will let you quickly understand how much more powerful the X is. Generally speaking, if you have a 1080p TV, the S will probably be all you need. The X only hits its full benefit when you start dealing with 4k resolution.