There's a lot of ways of taking screenshots, really.
You can try what Niicola said above, or you can use
this. It's a very small program that you install in your computer and you can use it to take screenshots very fast and upload them on the internet, and for that you just need to open your toolbar, right click the Puush icon and click Capture Area. After that, you just need to drag the cursor around the area you want to take a screenshot of. Wait a little bit for it to be uploaded, then paste the link on your browser (it will be automatically on your clipboard) and download the image to your computer.
Hope this helps.