A blackboard, or chalkboard, is a surface you can write on in chalk. Blackboards are usually used in classrooms or to write menus in restaurants.
A college is a place of higher learning, similar to a university.
You enroll in something when you are added to a list, or roll. Enrolling is usually used to mean signing up for some kind of course of education at a school or university.
Exam is an abbreviation of the word examination. An examination is a test or investigation of something. At school, you may take exams to test your knowledge. A doctor may give you a physical exam to check your health.
A principal is someone who runs a school, doing more administrative work than teaching. In some countries, a principal is called a headmaster or headmistress.
A school is a place you go to to learn things, like how to read and how to write. School is a very important time in your life. You will meet friends you might have for many, many years, and you will learn all the things you need to know as an adult.
A student is anyone who is actively learning something, usually by attending a school, college or university.
You study for something when you learn about it as much as you can, usually to prepare for something like an exam or writing an essay.