  This article is an introduction to some aspects of \'Ecalle's mould calculus,
a powerful combinatorial tool which yields surprisingly explicit formulas for
the normalising series attached to an analytic germ of singular vector field or
of map. This is illustrated on the case of the saddle-node, a two-dimensional
vector field which is formally conjugate to Euler's vector field
$x^2\frac{\pa}{\pa x}+(x+y)\frac{\pa}{\pa y}$, and for which the formal
normalisation is shown to be resurgent in $1/x$. Resurgence monomials adapted
to alien calculus are also described as another application of mould calculus.
