CRYSTALS is used for refinement of crystal structure models against diffraction data, and for analysis of the model and its fit to data and expected norms. Data is usually required from a single or twinned crystal sample, preprocessed into standard hkl format, along with relevant data such as unit-cell dimensions, radiation type and sample environment. CRYSTALS can be used to re-analyze data from the literature, where appropriate data files are available. CRYSTALS can read data from X-ray, neutron and electron diffraction experiments, although other software may be more appropriate for handling multiple scattering in electron diffraction data.
The CRYSTALS user guide is a good place to start for installation and a quick overview of the software.
The CRYSTALS reference manual) provides detailled syntax of CRYSTALS commands and data formats.
The CAMERON manual provides a reference for using the built-in crystal structure graphics tool CAMERON.