Please help, having a hard time answering this question or getting an idea

Two or more samples are often compared when we suspect that there are differences between the groupsfor example, are cancer rates higher in one town than another, or are test scores higher in class than another class? In your chosen field (Psychology), when might you want to know the mean differences between two or more groups? Please describe the situation (what groups, what measurements) including how and why it would be used.