There are three ways to take screenshot or capture your screen on Mac. Follow these steps to understand.
"Press" Shift + Command + 3, your entire screen will be captured.Your full screen will be captured, then select the location to save the screenshot.
To capture the full Screen
"Press" Shift + Command + 4Then, drag the cursor and select the part of the screen, which you want to capture.
To capture a part of the Screen
"Press" Shift + Command + 4, then hit the spacebar button.Your cursor will turn into a camera icon.
To capture a specific window on your screen
Hover the camera icon over the window you want to capture and click on it.Click on the "Option" button to choose the location of the screenshot to be saved.
The point to keep in mind is that if haven't updated to OS version Mojave or Catalina, then the screenshot will be saved on the desktop in PNG format.
You can also record screens on newer OS versions. Choose the screen record option from the screen caption bar. You can record the full or part of the screen.