There is tons of info on this; but, I will cover the basics.
Lower numbers = Rich
Stoich = "In the middle"
Higher numbers = Lean
It seems that most people tune for 11 to 11.5 for street/daily driving. 12 is pretty lean.
Personally, I am tuning for 11.5.
Again, this is VERY basic. Use the 'Search', do some reading, and absorb as much info as possible.