In practice, a confidence interval is used to express the uncertainty in a quantity being estimated. There is uncertainty because inferences are based on a random sample of finite size from a population or process of interest. To judge the statistical procedure we can ask what would happen if we were to repeat the same study, over and over, getting different data (and thus different confidence intervals) each time.
Know that a confidence interval computed from one sample will be different from a confidence interval computed from another sample.
Understand the relationship between sample size and width of confidence interval.
Know that sometimes the computed confidence interval does not contain the true mean value (that is, it is incorrect) and understand how this coverage rate is related to confidence level.