How do I do an "or" orperation for a search in Apple Mail?

You can use Boolean operators:

Use Boolean searches:

Use Boolean operators such as AND, OR, and NOT. For example, to search for messages that contain “yosemite” and “yellowstone” but not “teton,” type “yosemite AND yellowstone NOT teton” or “yosemite AND yellowstone -teton.” You must type Boolean operators in uppercase.

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If it's a one-time thing using the Boolean operators in the search bar as mentioned above will probably be the best/easiest way...

However, Rules and/or Smart Mailboxes will do the same thing (and a whole lot more), but would probably only be worth the time for things you search for somewhat often.

Click here for a pretty good article on Rules, Smart Mailboxes, and VIPs