If I have multiple people who are going to have email addresses with my website, can I put a special page that they can only access from my website. Like, a login where only people who have a email address and password can access it?

You can make a log-in page, check out http://www.coffeecup.com/website-access-manager/

Why would you need to password protect the login page? No one will able to open their email without a password specific to their own email account, so there is no real benefit to making them type a password to access a page where they have to type another password :-)

I have an email login for clients on my site but the page is open to anyone who wants to open it. It does them no good without a login:

http://www.sprucepinedesign.com