How to take / grab Screenshot:
Go to Right top search icon (spotlight) and search Grab.
How to measure pixel:
When you need to calculate even a pixel for your perfectionist client
Press CRT+SHIT+ 4
How to measure RBG:
When you have been asked to follow the exact color combination like Andorid / windows version by giving the sample / screenshot.
Go to Right top search icon (spotlight) and search ColorMeter.