Draw parallel line with distance

Hi … if I want to draw the line with a specified distance and parallel with that line what should I do? In the pic, there is a line and the distance is 100…

Line.ByStartPointDirectionLength should do the trick.

The start point is any point, but you may want to control it relative to the original line.
The direction is the direction of the line.
The distance would be 100.

the length is distance ?

Yes - how long the new line should be.