Open QuickTime Player
Click File
Select New Screen Recording
Click the arrow next to the Record button
Choose a microphone
Click Record
Select the full screen or drag to record a portion
Click Stop in the menu bar when finished
To record system audio, install a virtual audio driver or use a screen recorder that supports internal audio
Open the screen recording app
Enable system audio or internal audio in the audio settings
Start the recording
Stop the recording when finished
Save the recording file