  X-ray emission from cool stars is an important tracer for stellar activity.
The X-ray luminosity reflects different levels of activity and covers four
orders of magnitude in stars of spectral types M-F. Low spectral resolution
provided by X-ray observations of stellar coronae in the past allowed the
determination of temperature distributions and elemental abundances making use
of atomic databases (listing line emissivities and bremsstrahlung continuum for
a given temperature structure). The new missions XMM-Newton and Chandra carry
X-ray gratings providing sufficient spectral resolution to measure the fluxes
of strategic emission lines. I describe the different approaches applicable to
low-resolution and high-resolution spectra, especially focusing on the new
grating spectra with X-ray lines. From only a few lines it is possible to
determine plasma temperatures and associated densities, to check for any
effects from resonant scattering, and to identify particular abundance
anomalies. Line-based temperature- and density measurements represent only a
fraction of the total plasma, but the pressure environment of different
fractions can be probed simply by selection of specific lines. Selected results
are presented covering all aspects of line-based analyses.
