Quicktime isn't just a media player in Mac OSX, it's also a great way to record video, audio. and-in this instance-your screen!
Quicktime comes preinstalled in OSX. Open your apps and click it's icon for launch.
Next go to file and select 'New Screen Recording'.
The GUI pops up. If you like you can access some settings by clicking the down arrow to the right of the red record button.
Now, all you need to do is click the red record button.
This message pops up:
You can click once to record the full screen, or click and drag to record a specific area.
After clicking and dragging you can refine your selection by grabbing the handles before clicking to record.
Once you've completed the the task you want to record, look to the top right bar on your screen, and click the stop icon.
Shortly after, your new recording will open as a movie in quicktime.
All that's left is to save!
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