Click on the button to create line tangential to two arcs/circles. If any entities are already in the Selection Set they are deselected and the prompt reads:
Give First Arc/Circle To Blend at approximate Tangent point:
Select the first arc/circle which is changed to the highlight style and the prompt reads:
Give Second Arc/Circle To Blend at approximate Tangent point:
Now as the the cursor touches the 2nd arc/circle Draft it shows a preview of the resulting line. Move the cursor to the side of the of the 2nd tangent point and click. The new line is drawn.