If you would like to take a picture of your screen, it can be done in several ways.
How to take a screenshot of the entire screen:
If you want to take a screenshot of the entire screen, hold down SHIFT ⇧ + COMMAND ⌘ + 3 at the same time.
How to take a screenshot of a section of the screen:
If you want to take a screenshot of a specific area of the screen, hold down the SHIFT ⇧ + COMMAND ⌘ + 4 keys at the same time.