Open QuickTime Player
Click File
Select New Screen Recording
Click the arrow next to the Record button
Choose the microphone you want to use
Adjust volume if needed
Click Record
Select the full screen or drag to record a portion
Click Stop in the menu bar when finished
Save the recording when prompted
If you need system audio, install a virtual audio driver or use a screen recorder that supports internal sound
Open the screen recorder app
Enable microphone and system audio recording
Start the recording
Stop the recording when finished
Save the file