The Wikimedia Foundation requires that users confirm their email addresses before they can use email features. This prevents problems with fake addresses, such as bounced replies or spam.
You only need to confirm email addresses to use the email system; you can login and edit pages as normal without confirming your address.
You are not even required to enter an e-mail address at all to register; it remains completely optional (However, administrators are expected to have a confirmed email address).
You can check your address confirmation status in your preferences. If your account was registered prior to March 2, 2006 (when confirmation was enforced), your existing address (if any) has not been automatically confirmed. Accounts on multiple wikis will need to be confirmed individually. If you change your email address, you will automatically be sent a new confirmation email.
From your preferences, go to the section entitled Email, if desired check the box next to Enable e-mail from other users.
Click the button in that section; an email will be sent to your email address with a confirmation link.
When you receive the email, click the link it contains to confirm that you own the email address.