To change the appearance of a function's graph on the main plot window, select the function in the Functions sidebar. You can change the plot's line width, color and many other aspects by clicking on the Color: or Advanced... button at the bottom of the section Appearance.

If you are editing a Cartesian function, the function editor will have three tabs. In the first one you specify the equation of the function. The Derivatives tab lets you draw the first and second derivative to the function. With the Integral tab you can draw the integral of the function.