RonStarbuck,
Thanks for letting us know that you're working with a wired microphone. In that case, open up the System Preferences menu, and click on the icon titled sound. Once you've done that, click on the Input tab in the Sound menu to see the list of microphones available to use. This is where you want to select the mic you'll be using. If you're using a laptop, it will have a built-in Internal Microphone that is usually chosen by default. If you have headphones with a mic attached and plugged in, you'll see them listed as an External Microphone. Either of these will work, and you can test them by talking and seeing that the bars in the Input level fill up.
Change the sound input settings on Mac
If you're still unable to get your Mac to see your external microphone, can you tell us if you have tried checking the manufacturer's website for drivers that may need to be installed to get your Mac to detect your microphone? If not, please give that step a try, and let us know the outcome.
Thanks for using the Apple Support Communities.
Cheers!