When turned on, rotation lock (sometimes referred to as “orientation lock”) keeps your screen from rotating when you move your iPhone–like when you rotate your iPhone to the left, right, or upside down. Rotation lock will lock the orientation of your iPhone’s display in portrait mode (portrait mode is where you hold your iPhone with the home button at the bottom). Note that rotation lock does not let you lock your iPhone in landscape mode (landscape mode is where you hold your iPhone with the home button on the right or left).
Turning rotation lock on and off on your iPhone is really easy, and this post explains how to do it.
SimpleiPhone 