I'm using a Mac.

When I go to Audacity-Preferences-Devices, it won't allow me to select "Internal microphone" as a recording device. "Built-in Input" is the only option. I know my microphone is working. It even displays "Internal microphone" on the main Audacity menu next to the toolbars (upper right in the training video), it just doesn't allow me to select it under Preferences.