As with every sport, judo has a list of rules that must be followed in tournaments. In addition to the basic rules of the sport, there are also rules that apply specifically to certain belt levels and ages.
This sheet will show you any chokes or techniques that are prohibited during tournaments for the various belt and age levels.
Download the full file here: 2018-19 JO Tournament Regulations Matrix
For the rules of the sport, there are 2 PDF’s for you to read. The first is the official IJF Referee Rules. The other is a a smaller booklet that shows you what would constitute a penalty during a tournament.