I am making a backrest/sissy bar for my Harley Davidson. I am using this software to create the brackets for the sissy bar to attach to the motorcycle. That way I can print the technical shit at scale and use as a template to cut the metal with my plasma cutter.
How can I create this shape?? Thanks!
Best to give us more than one perspective please. By that In mean show us side and front.
Consider this (quick & dirty example). I lofted several segments by using the move tool to duplicate and resize a rounded edges rectangles. Then I mirrored that. :
There will be several way to achieve your goal. I prefer to give hints rather than lead by the hand. With Shapr, one must think outside the box, grasshopper. Shapr is not ideal at making organic shapes (like flowing bends) but it can be done with patience. Bends in one dimension a plasma cutter can handle. In 2 dimensions, I don’t think so. (Correct me if wrong please). You bar has bends in 2 dimension from what I can see. Someone else here will see it differently and perhaps have a better method to help you. 
Please forgive the result, rather focus on the method.
Here is another method using Sweep. Here I use a spline to create a shape in one plane and another shape in a plane 90°. When the 2nd body is subtracted from the first body, a curved edge in 3D space is created. You can use that edge as the path for the Sweep tool.
Here’s a variation of the example I did yesterday. I mirrored the 1st spline to create a symmetrical body and used Sweep twice.
