There are a myriad of reasons why you'd want to take a screenshot of what is currently on your computer's screen. Assuming you're using Windows, this is actually a very simple process.

Simply press the "Print Screen" button (sometimes abbreviated as "Prt Scrn") on your keyboard. Windows has now automatically copied an image of your screen to its clipboard where it is stored temporarily until it gets replaced by anything else (e.g. text in Word, etc.).

To save the snapshot that Windows took, you'll need an image editing program. You can use Windows' Paint application, but it, in a word, sucks.

Fortunately for you, there are quite a few nice free image editing applications available on the internet. You can do a search and experiment until you find one that you like, but to get you started, try out PhotoPlus 6.

After installing PhotoPlus (and after pressing "Print Screen" to grab an image of your screen to the clipboard) open the program. If a welcome screen greets you, click on "cancel" to make it go away. Now click on "Edit" and select "Paste as new image".

Now you can manipulate the image as you see fit and save it as a .jpg file when you're done!

PS: If you used a different image editing program than PhotoPlus, then the instructions would obviously be different, but the gist of what you need to do is:

1. Press "Print Screen";
2. Open image editing program;
3. Paste captured image;
4. Save image.