To center an object means to set that object as the pivot around which all camera movement will be fixed. This section goes over different ways to perform this function with all objects and clarifies the difference between centering an object in view and setting an object as the center.
To select a camera frame means to select a different frame in which camera position and orientation is fixed. All frames are fixed relative to the current central body. This section describes the four different camera frames available and details how to use each one.