Workplanes
A Workplane is a plane (whose use is optimal in the Perspective view) that can be freely positioned and used by Cinema 4D for snapping, positioning Spline points, arranging newly created objects and similar functions. Workplanes help when arranging or positioning elements across a plane. This is normally done by the world grid but there are instances in which alternative planes are required. Position, scale and rotation will always be based on the world coordinate system (that remains visible as a light gray grid). The only exception is that the Coordinates Manager shows these relative to the Workplane in World mode.
The Workplanes are primarily designed for use in technical modeling in which many elements are arranged perpendicular to a given axis - as opposed to organic modeling.
Regardless of how the Workplane is rotated or moved, the Default cameras will move accordingly in the orthographic views (as if they were fastened to the edge of the Workplane (or the Y axis of the Top view)). Hence, a move parallel to the grid lines will result in a move parallel (or perpendicular) to the Workplane.
Note the small world axes at the bottom left of each view (that still display the World coordinates), whose values change according to the modifications made to the Workplane (the 
Locked Workplane
Workplanes offer a frame of reference that can be modified freely. Workplanes have several commands and modes with which they can be modified to fit your needs. These are described in the following sections.
The numerous Workplane modes and their commands can be confusing. To return to the default settings (Workplane = World grid): Select the
Align Workplane to YThese 5 commands set the Workplane back to the respective default state and lock the Workplane. Hence, if you were working in Interactive Workplane mode you will be taken out of this mode.
Use these commands to arrange the Workplane to the respective axis. The Normals will be oriented in the direction of the Y axis, which is the same as the World axis. Align Workplane to Y is the most commonly used mode because it reflects the World grid.
This command rotates the Workplane to the currently selected element. For an object in Use Model mode this would be the XZ plane; in Use Polygon mode with a polygon selected it would be the polygon surface; in Use Point mode with 3 points selected it would be the plane created by the three points. In short, if a plane can be created by the selection in one of these modes (e.g., 2 bordering polygon edges), the Workplane will snap to it. Otherwise a position based on the average position and rotation of the selected elements will be used.
This command positions the selected elements (only the modeling axis for selections in component mode) on the Workplane (they will be arranged perpendicular to the Workplane). Objects will be rotated so that their axes lie parallel to that of the Workplane.