Select a pencil from the Pencils brush category, remember you can use your canvas to test these pencils out before you begin. Either open a new canvas and try them out, or test on the Cloned copy. Turn off the Tracing Paper to reveal the white canvas. If you choose Cmd/Ctrl-T (Select All) followed by Backspace/Delete this will clear your strokes.
The next step is to begin your pencil sketch. With the tracing paper image as your reference and using your selected pencil variant, make a quick line sketch. I want to emphasize that you don't really need to worry too much about detail. You are just forming your basic loose framework over which to build your painting. From time to time, toggle the tracing paper to see what you have drawn. When you have completed your pencil sketch, choose File > Save As. Remember to save sequentially.