Here's the video explains how you can take a screen shot of your iPhone 4 with in 3 minutes. Also works with iPod Touch.

How to Take a Screenshot with Your iPhone?

Watch the video here:

While looking at the screen you want to capture, just click and hold the top power button and the round menu button simultaneously. Your phone will take a picture of the screen and store it in your Camera Roll. Now you can send it, text it, download it, etc.