Windows 7 doesn't ship with an e-mail client. You'll need to add one to be able to start using E-mail.
If you just need a basic e-mail client Windows Live Mail 2011 is a good choice and it's free. Windows Live Mail 2011 download
There are some other free Windows Live software packages you might be interested in as well. Windows Live Essentials 2011
Live Mail is also a part of this Essentials package too.