Once selected the Ribbon changes to show the current dimension properties and the command prompt reads:
Give first point of box to select points:
Select the first corner point of the selection box using any of the snaps and input options. (Generally this would be a screen position). The prompt now reads:
Give second point of box to select points:
As you move the cursor the a dynamic (dashed line) selection box is displayed. Select the second corner point of the box using any of the snaps and input options. (Generally this would be a screen position). Place this other corner so that the box encompasses all of the points to be dimensioned. The prompt now reads:
Give Dimension Point (H)orizontal or (V)ertical:
The dimensions are created in either the horizontal or vertical plane. You can force which plane to us by pressing the H or V keys.
As you move the cursor a dynamic representation of the dimensions is attached to the cursor. Simply move to the desired position and click into place.