...

1. Select the tool, then snap to the center of the first circle.
   
2. Move the cursor. Notice that the preview of the construction line is parallel to the line you are dragging out.
   
3. Snap to the center of the other circle to set the construction line.
   

Construction-Bisection

Creates a construction line which bisects an angle

1. Click on the first point. this will be thevertex of the angle to be bisected.
2. Click on the second point. this will be the first edge of the angle to be bisected.
3. Click on the third point. this will be the second edge of the angle to be bisected.

Image Added

1. 1. Move the cursor. Notice that the preview of the construction line is parallel to the line you are dragging out.
      Image Added
   2. Snap to the center of the other circle to set the construction line.
      Image Added