Forms, or kata in Japanese, are a simulated, sequence of moves designed to develop the basic martial arts movements. Forms help students work on the key stances (e.g. front, back, and horse stance) and blocks (e.g. low, high and middle block). Perhaps, most importantly forms are synchronized patterns of movement that are done in a group setting, building teamwork and comradery.
When one is first introduced to a form, it seems that the movements are very hard to remember. Learning the moves can be frustrating, but it trains the mind as well as the body in certain movements that are used throughout karate. As you learn more forms, you will notice similar patterns allowing a martial artist to pick up new forms very quickly.
There are many benefits to learning forms. First, and foremost, they help martial artists learn the basics and build muscle memory as well as focus. They also enable students to track their progression as forms take on various levels of difficulty. As a student works up through the belt system, he will learn and conquer increasingly more difficult forms. Finally, when done with vigor, forms can be an excellent form of exercise.
As you prepare for your belt test, recognize that the form you are learning is just one in a sequence of forms that you will be mastering over the course of your martial arts career.