There are two methods of practicing Judo, kata (pre-arranged forms) and randori (free practice or sparing). Kata consists of various informal drills, including uchi komi (practicing entering for throws), nage komi (practicing throwing), and mat work drills (pins, armbars, strangulations, and escapes). These informal kata or drills are essential for learning proper application of techniques. Kodokan Judo has 9 formal kata designed to teach and demonstrate specific techniques.
Kata - form practice
Randori (free practice or sparing) prepares students for competition and allows you to feel what the techniques feel like against a resisting opponent, and helps you hone in on what you need to work on.
Judo techniques range from basic body control to advanced throwing, grappling, and striking techniques. The techniques of Judo are separated into a number of categories:
Tai Sabaki - Body movements
Ukemi - breakfalls
Nage waza - throwing techniques
Katame waza - grappling techniques
Atemi waza - striking techniques
Note: Traditionally and for safety, Judo only practices striking techniques in kata (pre-arranged forms) and not in randori (free practice or sparing) nor shiai (competition).