Taking screenshots on the Nexus 7 tablet is a snap. In fact, taking shots on any device running version 4.0 (Ice Cream Sandwich) is the same physical button combination.
All you have to do, once you have the image you want on the screen, is to keep the power and volume down buttons pressed at the same time. It might take a few attempts the first time you try it, but once you get it down, it’s easy.
You’ll see a frame appearing on the screen, and the resulting image will be saved in your Gallery.