There are two major ways that Judo can be learned and practiced: Kata and Randori. Or, put another way, you can learn by going through a set of techniques where the outcome is known called Kata. Or you can learn by practicing techniques that best suit you personally and then practice applying them in live-action where it is perfectly safe but allows for learning in a dynamic way called randori.
Typically, students must begin by learning the basics of posture, movement, footwork and techniques. They work on applying the techniques in randori. Later, when they have a basic understanding, they can begin to learn Kata.
Forms (kata) are pre-arranged patterns of attack and defense, which in judo are practiced with a partner for the purpose of perfecting judo techniques. More specifically, their purposes include illustrating the basic principles of judo, demonstrating the correct execution of a technique, teaching the philosophical tenets upon which judo is based, allowing for the practice of techniques that are not allowed in competition, and to preserve ancient techniques that are historically important but are no longer used in contemporary judo.
Knowledge of various kata is a requirement for the attainment of a higher rank.
There are seven kata that are recognized by the Kodokan today:
There are also other kata that are not officially recognized by the Kodokan but that continue to be practiced. The most prominent example of these is the Go no sen no kata, a kata that focuses on counter-attacks to attempted throws.
Judo emphasizes randori which sort of resembles free-style sparring as one of its main forms of training. Part of the combat time is spent sparring standing up, called tachi-waza, and the other part on the ground, called ne-waza. Sparring, even subject to safety rules, is much more alive than only practicing techniques on their own, which is what jujutsuka were used to doing. Using full strength develops the muscles and cardio-vascular system on the physical side of things, and it develops strategy and reaction time on the mental side of things, and helps the practitioner learn to use techniques against a resisting opponent. A common saying among judoka is “The best training for judo is judo.”