These z-table and the t-table are well-known and have been developed by statisticians for the uses of testing.
The combined numbers in first column and first row of the z-table are the z-scores. The values in the middle of the table are the areas or probabilities that Z is less than the specified z-score. The probabilities are the integral from negative infinity to the z-score of the function of standardized normal distribution shown below (which is above the z-table).
The t-table also presents the t-scores and probabilities related to it. However, the t-table has different way of presenting the t-score and probabilities. The values in the middle are the t-scores whose tail areas are on the top rows and degrees of freedom on leftmost column. The marked value 2.262 is the t-score whose area to the right is 0.025 (area to the left is 0.975) with degrees of freedom 9.
Hope this helps.
The 365 Team
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