.Mac is Apple's set of web tools for email, website hosting/creation, bookmark, calendar, and address syncing, and online disk storage. It is $99/year. It is up to you whether or not those services are worth the money. The webmail is well done, and the integration with your mac is very good.
However, if you simply want to do email, there are a number of providers that will give you an address either free or fairly cheap. I believe Yahoo offers a paid POP access (which just means that you can use an email program like Mail or Entourage to check your email) as well as Google's Gmail service. Outside of those two big contenders, there are lots of smaller companies that offer email. I use a service from macosx.com for my email account - it's something like 15 bucks a year for pop/webmail email.