For a new user, getting started using an event generator can be a daunting task. PYTHIA attempts to describe all parts of high-energy collisions between several species of fundamental and composite particles, and must by definition contain many settings and possibilities, which are not neccesarily interesting or useful to a new user.
PYTHIA therefore ships with several example programs, each
highlighting one, or a few, aspects of the framework. All example
programs are located in the examples/ subdirectory, along
with instructions on how to be run.
A new user who is already familar with other event generators, might want to start reading through the description of the Program Flow, and then proceed to browse through the Example Main Programs, to find the physics aspects the user desires to study.
For completely new users, the separate PYTHIA 8.3 Worksheet, offers a more suitable practical introduction.