Print Screen is a Windows keyboard key dedicated to capture the whole screen upon pressed. If you look at the upper right side of a windows keyboard you will find this key labelled as "Print Screen" or "Prt SC". As the name suggests, it captures the entire desktop screen and prints it into the clipboard which you can paste anywhere into an application or a file on Windows. Surprisingly, there is no "Print Screen" button on your Mac keyboard but that does not mean that you can not Print screen on Mac.

There are multiple ways to Print Screen or take screenshot on Mac
1. You can press and hold the Shift+Command+4 keys and drag the area to take the screenshot of. The screenshot will be saved on the desktop by default.
2. You can use inbuilt grab utility to take screenshot on Mac
3. You can even use Preview to take screen shot or Print screen on Mac
4. You can also try the Terminal command for screen shot.

There are different option that you can manage using terminal that affect the behavior a Mac takes screenshot or print screen.

How about taking the screenshot of an entire webpage

Obviously, you will not be able to Print Screen the full web page using Grab or Keyboard shortcuts as mentioned above because they will only capture or print things that you see on the screen at a time. And a long web page can't fit to the screen and you will need to scroll it. But don't worry taking screenshot of long web page is also possible with the help of third party tool.There are various paid and free tool. Snagit is one of the famous paid software compatible for both Mac and windows which can take the screenshots of a long web page.

You can read this interesting article in full at http://www.hawkdive.com/2017/07/print-screen-on-mac.html whic has put all the ways to print screen on Mac together very nicely.