Open QuickTime Player
Click File
Select New Screen Recording
Click the Record button
Choose to record the entire screen or a selected portion
Click Record to start
Click the Stop button in the menu bar to finish
Save the recording when prompted
Or press Shift + Command + 5
Select Record Entire Screen or Record Selected Portion
Click Record
Click the Stop button in the menu bar to end the recording
Open the saved video file from the desktop or chosen location