How do I calculate a confidence interval when I know the sample mean and standard error?

To calculate a confidence interval with a known sample mean and standard error, use the formula: Confidence Interval = Sample Mean ± (Critical Value * Standard Error). The critical value depends on the desired confidence level (e.g., 1.96 for 95% confidence, 2.576 for 99% confidence). The standard error represents the variability of the sample mean. Ensure you're using the correct critical value corresponding to your desired confidence level and the appropriate t-distribution if the population standard deviation is unknown.