[1] First create a new document of 400*400, as shown in the figure.
[2] Select the Rectangular Marquee Tool.
[3] Set the foreground color to red, as shown in the figure.
[4] Use the Rectangular Marquee Tool to create a rectangular selection, and then fill it with the foreground color, as shown in the figure.
[5] Select the Polygonal Lasso Tool.
