Mathematica's unified symbolic graphics architecture makes it possible to mix programmatic graphics generation with interactive editing and control. The Mathematica Drawing Tools palette lets you edit existing plots or illustrations—or create free-form ones from scratch.
You can edit Mathematica graphics by using the tools in the Drawing Tools palette.
To create a new graphic, click the new graphic button in the Drawing Tools palette. The orange box that appears in your notebook indicates that an empty graphic has been created:
You can also change the attributes of graphics, such as color, thickness, and arrowhead shape using the Drawing Tools palette.
Click the object whose attributes you want to change, and then use the controls under the Stroke section to change thickness, color, or other attributes. Here, the sine curve was clicked and then changed to a thick red line: