What prerequisites should students have the knowledge of before calculating the confidence intervals for two population means?

What is the difference between the different confidence interval formulas?

A random sample of 100 m&m's produced 17 green m&m's.  What is the point estimate for the population proportion of green m&m's?  Construct the 95% confidence interval for the true proportion of green m&m's

If a 90% confidence interval for the difference of proportions contains some positive and some negative values, what can we conclude about the relationship between p1 and p2 at the 90% confidence level? There is a positive difference between p1 and p2. There is no difference between p1 and p2.     There is a negative difference between p1 and p2. We cannot make a conclusion about the relationship between p1 and p2.