As a “complete beginner” you should not start with an “advanced” model like the core-shell polarization model. You should first build your general LAMMPS and MD simulation skills with much simpler models, so you can better assess whether any issues you encounter (and there will be issues with advanced models) are due to lack of understanding or bad choices or settings, parameters or geometry. Thus I strongly recommend you start your LAMMPS journey with the tutorials at https://lammpstutorials.github.io and do not proceed to core-shell models until you are comfortable with creating and running simulations with LAMMPS.
The next steps would then be to study the information available in the LAMMPS manual and the corresponding examples in the LAMMPS source distribution. Again, I strongly advise against jumping ahead; it will just make everything more painful and likely filed with more errors and frustrations.