"Mail feature" in macbook

I am a recent convert to mac.I just got my new black macbook. pc days are just about over.
but i do have a question about the mail feature...
It bothers me that someone can read my mail if they are using my computer. Is there a way to program it so that there is an extra password???
Or how do you just cancel the mail feature?
it bothers me since others might be using my computer in my absence...
Thanks!!!

Password protect your account and don't share the password, make sure you lock or log out of your account when you leave it and turn on the password requirement to log into an account when booting it.. Create a guest account for others to log into.