Golf balls have a core that is generally made of rubber and then they have between three and five layers. Each layer provides a performance characteristic for a specific type of shot. Example: one layer may activate for a driver while another may activate for a wedge.
The most important part of a golf ball for players to understand is the cover. It is usually made of either urethane or surlyn. Urethane is a higher quality softer material made for premium golf balls, such as the Titleist Pro V1. Surlyn is a harder material made for less expensive golf balls. The main difference between the materials is that the softer urethane provides higher spin off of the shorter clubs whereas the harder surlyn provides more distance off of the drivers but not as much spin.
For beginning players surlyn is a good starting point to use until their swings become consistent.