An XSTAR session consists of several basic steps: initial setup, model calculation, and final printout. The initial setup consists of the input of various parameter values necessary to specifying a model, reading in atomic data files, and the program's internal initialization. The model calculation consists of the calculation of ionization, excitation, and thermal equilibrium, and radiation transfer (as described in Chapter 9) at each of a number of spatial grid points. After the model calculation various quantities are output, and the program terminates. The details of the input parameters are described in Chapter 4, and the output is described in Chapter . Note that both of these have changed significantly since version 1. In this chapter we describe general features of the XSTAR operation which are important to the user.