  In this tutorial it is explained the procedure to analyze an optical
emission-line spectrum produced by a nebula ionized by massive star formation.
Particularly, it is described the methodology used to derive physical
properties, such as electron density and temperature, and the ionic abundances
of the most representative elements whose emission lines are present in the
optical spectrum. The tutorial is focused on the direct method,based on the
measurement of the electron temperature to derive the abundances, given that
the ionization and thermal equilibrium of the ionized gas is dominated by the
metallicity. The ionization correction factors used to obtain total abundances
from the abundances of some of their ions are also given. Finally, some
strong-line methods to derive abundances are described. These are used when no
estimation of the temperature can be derived, but that can be consistent with
the direct method if they are calibrated.
