Complex sentence: A "kickstart" file consists of a series of options to be passed to the Anaconda installer which describe how to setup the system, optionally it may include custom scripts to be run before and/or after the installation.
Split into simpler sentences: A "kickstart" file contains a series of options, to be passed to the Anaconda installer, that describes how to set up the system. It may also include custom scripts to be run before or after the installation.