Different tools can help us do reflections, and tracing paper is one of them.
In this video, I'll show you a shape, and ask you to reflect that shape over a given line. I'm using a diagonal line; the process is exactly the same if you use a horizontal or vertical line.
I'll encourage you to try to imagine where the image will be and how it will look. Then I'll show you how to use the tracing paper to reflect the pre-image. I'll also show you a few ways you can double-check your work.
I actually used parchment paper instead of tracing paper because that was what I had on hand.