You need to find out whether you can use POP/IMAP servers to get your school mail, and what they would be. For example, if you have POP access, the server name might look like "pop.myschool.com" or "mail.myschool.edu" - something like that. There may also be specific port numbers or security settings that you need to use. Check with your school's IT department.
Usually when you set up a new account, you'll enter the email address - if Mail can't work out the server name automatically, it will ask you for the server details.
Let us know how you get on.
Matt