The workplane can also change when you select objects, depending on whether the 2D or 3D Selector is used. See 2D - 3D Selector.

Workplane by View

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Sets the workplane according to the current view.

Position the model to the desired view. In this example, the current workplane is By World.
Select By View. The workplane is turned so that it is parallel to the view plane. The Z axis becomes perpendicular to the drawing screen.

Workplane by World

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Sets the workplane based on the WCS (World Coordinate System).

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You can display the WCS at the lower left corner of the screen by opening the Preferences and checking Show World CS.

By World, top view

By World, Isometric_SW view

Workplane by Entity

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Sets the workplane according to the coordinate system of a selected object, block, or group.

Click By Entity, and the cursor becomes a dashed representation of the current UCS. Click the desired object.

The workplane is placed along the plane on which the object was created.
To change the workplane to another object, use the tool again. Click the desired object.

The workplane is positioned according to the selected object.

Tip: If an object is listed in the Graphics section of the Design Director, you can set the view to an object's Workplane by Entity, and set this workplane as the current workplane. See Design Director- Graphics.

Workplane by 3 Points

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Sets the workplane to fit three points. You can select these points, or enter their coordinates in the Coordinate Fields.

Select the UCS origin.
Select the second point to define the +X direction.
Select any point that lies on the desired X-Y plane.

The workplane is created.

Workplane by Z axis

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Sets the workplane by defining the Z axis of the UCS. The X-Y plane is perpendicular to this axis.

Select the UCS origin, or enter the coordinates in the Coordinate Fields. In this example, the workplane is to be aligned with face shown.
Select the second point to define the +Z direction.

The workplane is created.

In this example, because of the view, it may not appear that the workplane was aligned correctly. You can rotate the model to verify that the workplane is indeed aligned with the desired plane.