From you description is sounds like you are using "Windows Search" (which shows "Best Matches" at the top of the results and includes files, etc.) - not Outlook Search.
How to use Outlook Search depends on which version/type of Outlook you are using. Without knowing that, all I can offer is: Open the Outlook app/program. Look for a "Search" or magnifying glass icon next to an input box. i.e. Use the Search box IN Outlook. Not the Windows Search box on your Desktop.