For an overview of how catSim is supposed to work, see this page.
For an overview of what source code is where, see this page.
For an overview of the contents of the UW LSST database, see this page.
To see a list of the getters (i.e. the columns that the catalog simulation knows how to calculate), see this page.
To learn how to query OpSim using the catalogs framework, see this page.