Outlook on the web (Office 365): https://support.office.com/en-gb/article/connect-email-accounts-in-outlook-on-the-web-office-365-d7012ff0-924f-4f78-8aca-c3912d886c4d
Outlook desktop application: https://support.office.com/en-us/article/Add-an-email-account-to-Outlook-6e27792a-9267-4aa4-8bb6-c84ef146101b
If the link is no longer applicable, please search the phrase "Add an email to Outlook" under Microsoft's Support Page at: https://support.office.com/