Press Shift + Command + 5
Select Record Entire Screen or Record Selected Portion
Click Options to choose microphone, save location, and timer settings
Click Record
To stop recording, click the Stop button in the menu bar or press Command + Control + Esc
Open the saved file from the location you selected
Use QuickTime Player if you prefer: open QuickTime Player, click File, then New Screen Recording
In QuickTime Player, click the Record button, then choose the screen or portion to record
Stop the recording from the menu bar when finished
Save the recording when prompted