Usually one shot per animal target, if you miss its a zero and some time spent looking for the arrow! I also just started shooting 3D and leagues, here are some GREAT sites that helped to answer my questions. Once you understand these two different sets of rules it will be easier to understand the rules when you attend clubs that have slight variations. Hope it helps, set aside some time, probably 20 mins max for these two sites.
http://www.asaarchery.com/rules2008/parules.pdf - ASA Rules
http://ibo.net/Rules/ - IBO Rules