Given a random variable x with a Gaussian probability distribution function of mean µ and standard deviation σ, we can normalize it by considering a transformed, and also Gaussian, random variable z=(x-µ)/σ with mean 0 and standard deviation 1.

The table gives the probability that z is lower than the given number; as you can see, values lower than -4 or greater than +4 aren't interesting.

Regarding the values, study calculus and you will be enlightened. Sorry, there is no shortcut.