In the section "The Game", and into "4 Regular Skills", there was an error which you input Annie's Incinerate which shoots a AOE firewall instead of the fireball, which is meant to be "Disintegrate".
"Annie's Incinerate that launches a powerful fireball at an enemy dealing huge damage"

Besides the errors, the guide is very nice and could use some extra tips and tricks.

Quite a nice guide for absolute beginners! I do have a few complaints, tho.

• First off, you should probably try to make the guide look a bit more attractive. Consider adding some images, banners, and fix some BBcode.
  
• You have unclear wording at places, for example: "A tower counts you as "attacking an enemy champion" every time you deal damage to them"
  
• You forgot to mention support champions, yet you mention the concept of jungling. You should probably at least mention supporting as something best done with more experienced teammates.
  
• Doubt a lot of people come into this game from FPS games. Try comparing the leveling system to an RPG game.

Otherwise, deserves a +1!

I really like your guide, it is reasonably in-depth, very friendly to newbies and objective.
If I would say anything that could be improved I would suggest adding some example builds on the cheat sheet and going over then a little bit. Or just add an item section to explain some of the items. Good Job!