By default, the print screen button will capture the entire screen displayed in Windows. If you have 2 or more monitors, the print screen button will capture them all in one image.
1. If you want to capture a focused window only, hold ALT and press print screen. For example if you have an Internet Explorer browser window open, make sure it's focused by clicking on it, and then press ALT + Print Screen and this will capture JUST the IE window, not the entire screen(s).
2. Open up Paint (START > ALL PROGRAMS > ACCESSORIES > Paint) and press CTRL + V to paste the image into paint and you can then scale/crop/edit the image and save it as an image file.
3. Alternatively, you can use the Snipping Tool (START > ALL PROGRAMS > ACCESSORIES > Snipping Tool) and this will allow you click and drag an area that you want to take a screenshot of. You can then save the custom screen shot using the Snipping Tool application.