Print screen (often abbreviated Prt Scr, Print Scrn, Prt Scn, Prt Sc, Prt Scrn, or Prnt Scrn) is used to capture an image of what you see on your monitor as is. There are several software sold online to do this. However, for most purposes, you do not need to buy any software. Both Windows PC and Mac OS comes with the ability for Print Screen.

Almost all Windows keyboard comes with the Print Screen key. The key may appear differently depending on the manufacturer of your Windows keyboard. In some cases it is shown in its abbreviated form (Prt Scr, Print Scrn, Prt Scn, Prt Sc, Prt Scrn, or Prnt Scrn). However, as shown in the image above, the standard position would be at the upper right hand corner of your keyboard. The sole function of this key is to take a snapshot or picture of your computer screen and copy it to the clipboard (the clipboard is an invisible holding area for content that is copied). Its the same thing as if you copied something from a document and it is now on your clipboard waiting to be pasted in its final destination.
To save that image, first you have to paste it to a graphics editing program like Paint Shop or Photoshop. If you do not have a graphics editing program, you may just open a Microsoft Word document. Then press Ctrl + V to paste the image from the clipboard. That is it.
In a Mac keyboard, there is no Print Screen button. This makes it a bit challenging, but not impossible. Follow the steps below and to do a screen capture in Mac OS X.
Hold down Apple key ⌘ + Shift + 3 and release all
You can also do a screen capture for a portion of your screen. For that, follow the steps below:
Hold down Apple key ⌘ + Shift + 4 and release all key
Enjoy!!!