Windows has always had a feature called Print Screen. It is a key on your keyboard. When you press that key, a picture of your screen is stored on the clipboard. Read about that in another section of this site.
Windows 7 brings a new and better kind of picture taker. It is called Snipping Tool. You can find the snipping tool under Accessories in your main menu at the startup globe. Snipping Tool allows you to draw a rectangle of any portion of your screen that can be copied to your clipboard. Then that can be pasted into a Word document or an email.
This can be a very useful tool. An example is those times when you see a message on your screen and you can not print it. You can use the Snipping Tool to take a picture of it and then send it to a technical consultant to ask for help.