If you're new to Quest, you'll want to first check out our New Player Guide. That will guide you through the introductory steps!
You Don't Need to Learn All the Rules!
That probably comes as some relief. . . . There are many sections here, but not all of them will be relevant to you.
The first section (after this one) is Character Creation. This is a list of all the skills that can make up a character. You don't need to learn all of these skills–only the ones that your character actually has. (So if you don't buy Alchemy for your character, you don't need to understand how the Alchemy skill works.)
The next section is the Rules of Gameplay. These are the operating rules that conduct how a Quest event happens. You will need to read through and understand these, since they apply to everyone.
There's also a section on what's "in-game" (happening to your character) and what's "out-of-game" (happening only to you, the player). This will be useful for understanding how to make a Quest event seem more real.
After that comes the list of Spells. If your character can't cast spells, you can skip this (although it never hurts to learn how some spells work, because they'll be cast at you!). If you can cast spells, you'll want to understand the spells you have access to.
After that, you'll find information on Quest's major game world, the Continuing Game. You will want to skim this over and see if it helps you form your character's story and personal history–but you don't need to memorize it.