Q: How do I make a screen capture for research on my Mac computer (version 10 .10 .3?

Press the Shift, Command, and 3 keys to capture the whole screen.

Press the Shift, Command, and 4 keys to capture a draggable part of the screen, or follow it with the spacebar to capture a window.

Open the PNG on the desktop. Alternatively, combine either of the above with the Control key to put the screenshot onto the clipboard instead of the desktop.

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For info:

https://support.apple.com/en-us/HT201361