Outlook for Mac provides searching at various levels of complexity. Here are two methods that many find useful.

Quick Search (one mail folder, but can be modified)

You can search for a particular message by clicking on the folder where the message is stored, then using the search bar at the top of the Outlook window. This method searches only the folder you've selected. It does NOT include sub-folders of that folder (but see the bullets below).

While typing in the search box, you'll be offered the option of specifying where in the message to search (from, to, subject, etc.). If you do not select any of these specifics, Outlook will search all the basic headers, the subject, and the body of the message.

To return to a full view of all messages, click the X icon next to the search text box.

Advanced Find (multiple folders, more options)

Advanced Find offers more detailed options for locating items.

From the Edit menu, choose Find, then Advanced Search.

A Search dialog box will drop from the Search bar at the top of the Outlook window. Fill in the field or fields associated with your search.

To see additional criteria, click Add more options.

Multiple criteria are treated as "and" statements, that is, a message will be displayed only if it matches ALL the criteria you've specified.

To return to a full view of all messages, click the X icon next to the search text box.