Here is how to take a screen shot:
1) Press the "Print screen" button on your keyboard to take a picture of the current screen.
2) Open paint.
3) Press Ctrl and V to paste the image.
4) Save it.
If you want to post the image:
1) Create a Photobucket account.
2) Click the "Upload images & videos" button on your homepage.
3) Select the screen shot you took.
4) The image will then be Uploaded onto the site.
5) Click the "Save and get links" button.
6) Use the IMG Code to post the image.
Here's an example of a Screen shot: