Open Outlook and make your way to to the 'File' section and select 'New Account...'
In the pop up window enter the email you'd like to add
You may be asked to enter your password and then the account is added straight away if your email account is a Microsoft account. If not you'll be greeted with the page below...
Most enterprise accounts would be added using Exchange. And if your account ends in @Gmail or @yahoo then choose those respective options. But most of the time IMAP is needed
Depending on your email settings you may need to just give your password or you will need to enter your email server details like in the screenshot below
Contact your host if you don't know these details