The One Sample Z-Test Calculator determines whether a sample mean significantly differs from a known population mean when the population standard deviation is known. It computes both the z-value and the corresponding p-value based on the entered sample data and tail type. This test is widely used in statistics to evaluate hypotheses about population parameters, particularly when the sample size is large or the population variance is known. By analyzing the p-value, users can assess whether to reject or fail to reject the null hypothesis, providing insights into the statistical significance of their sample results.