  We describe the method for extracting the elastic scattering phase shift from
a lattice simulation at an introductory level, for non-lattice practitioners.
We consider the scattering in a resonant channel, where the resulting phase
shift delta(s) allows the lattice determination of the mass and the width of
the resonance from a Breit-Wigner type fit. We present the method for the
example of P-wave pi-pi scattering in the rho meson channel.
