Dr. Urroz's Tutorial may be the one to start with. It has chapters on different topics. One advantage of an environment such as wxMaxima is its ability to plot information quickly. A student needs to realize that there are several parts to plotting/graphing. Is one in 2D or 3D, are you using cartesian coordinates (2D or 3D), polar coordinates (2D), cylindrical coordinates (3D), spherical coordinates (3D), or a parametric representation (2D or 3D)? Although this may seem confusing to the novice it is to point out that there will be different "commands" that one will have to enter in wxMaxima depending on the context. One of the best ways to negotiate that hurdle is to find a few dedicated tutorials and keep them close to you.