Parallel line
The Parallel Line 
tool allows you to
create a line that is parallel to an existing line in your drawing.
Using the mouse
Select the Parallel Line tool and click on the line to which you want to draw a parallel line.
Move the mouse to set the side on which the parallel line will be drawn, and click to set the offset distance.
Using the keyboard
After selecting the Parallel Line tool and type in the offset distance.
Move the mouse to set the side on which the parallel line will be drawn, and click to place the parallel line.
Holding down the Ctrl key while placing the offset distance will draw parallel lines on both sides of the existing line.