If an app requests access to your mic or camera (for Zoom, Google Hangouts, etc.), you can give it permission in your System Preferences.
Open your System Preferences by clicking the apple icon in the top left corner of your screen and choosing "System Preferences..."
From System Preferences, open Security & Privacy
If your first System Preferences screen does not look like this, you will need to use the back button in the top left to get back to that screen
In Security & Privacy, click the lock in the botton left of the window
Enter your computer login or administrator password and click "Unlock"
Once unlocked, you may select Camera, Microphone, or whatever feature the app is requesting access to use from the left side of the window
Once the feature is selected, you may check off the applications that you would like to give permission to use that feature in the middle pane