to take a screen shot, you press the print-screen button and it will capture what is on ur screen at the exact time you press the button. The print-screen button is on the top row of keys on most keyboards..it will say something like "print scrn" or "prtscn"...after you have pressed the print screen key, you will need to open up a program that allows you to work with images...microsoft paint is a good and easy program to use for this purpose...so after you open up paint, you need to paste your image in..you can do this 2 ways:
1- right click and select paste
2- at the top of the screen, click edit, then paste
Now your image should be on the screen...don't forget to save your image before closing out paint (or whatever program you are using)
So, heres the list of steps again so you don't have to re-read the post above:
1- hit the print-screen key on your keyboard (Prnt Scrn, PrtScn, etc...)
2- open a program so you can paste your image (Paint, Word, Picture Manager, etc...)
3- select Paste
a: right click and choose paste
b: click edit, then paste
4- DON'T FORGET TO SAVE YOUR IMAGE
Hope this helps xD