The Nexus 7 changes the screen orientation based on the way you hold the tablet. Depending on how you’re using it, you might want to lock the screen in place.
Say, for example, that you want your screen orientation to stay in landscape. Swipe your finger down on the top right side of your tablet to pull down the menu.
Tap Auto Rotate and you’ll see that the button changes its name to Rotation Locked. Now the orientation is locked to the one you have at the moment.
Of course apps that run in a specific view will continue to do so — Temple Run 2 for example.