Graphical introduction to classical Lie algebras

We develop a graphical notation to introduce classical Lie algebras. Although this paper deals with well-known results, our pictorial point of view is slightly different to the traditional one. Our graphical notation is fairly elementary and easy to handle and, thus provides an effective tool for computations with classical Lie algebras. More over, it may be regarded as a first and foundational step in the process of uncovering the categorical meaning of Lie algebras.