Right-click on the message that isn't junk and select Junk email then select either Add sender to safe sender list (applies to the email address of the sender only) or Add sender's domain to the safe sender list (applies to all those email address that have the same domain, for example if you had an email from abc@microsoft.com, applying this would mean all future emails from senders with email addresses that end in @microsoft.com would be considered safe).
On the Home tab click on the dropdown menu marked Junk to see more detailed junk/phishing etc. options.