In the App list, tap Settings, and then tap Email + accounts. 

Do one of the following:

If you have Windows Phone 8 or 8.1, tap Add an account > Exchange.

If you have Windows Phone 7 or 7.5, tap Add an account > Outlook.

Enter your full email address and password, and then tap Sign in. If the phone finds your account settings, your email, calendar, and contacts will be synced to your phone.