There are a bunch of links you can use. This one is a good starter. The standard deviation is like the "center by which most samples hover around in a population". Those ZScores will tend to be under 1 and greater than -1 which means 1 standard deviation above the mean or 1 standard deviation below the mean.
Z-Scores Can Help Us Understand…
How typical a particular score is within bunch of scores. If data are normally distributed, approximately 95% of the data should have Z-score between -2 and +2. Z-scores that do not fall within this range may be less typical of the data in a bunch of scores. Z-scores are used in statistics to measure an observation's deviation from the group's mean value.Z-scores reveal to statisticians and traders whether a score is typical for a specified data set or if it is atypical. Basically Zscores >= 2 or <= -2 can be considered outliers/significant. 95% of your population falls within a Zscore of 2 and -2. Anything >= 2 is considered a big deal. Zscores help to measure the significance
Can a zscore larger than 3 exist? Yes
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