[HelloNurse]

For a definition of what the tables are about see the example on that site, it's worded casually but actually formal and precise. The values are obtained by computing integrals to find the area under a portion of the Gaussian curve (negative infinity to z or z to positive infinity). These particular integrals are traditionally called error functions.

[caribeaz]

Umm..can you ELI5 this a bit for me?

[HelloNurse]

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.