College is an educational school where people go to learn and earn an academic degree upon graduation. The requirement to enter college varies by country, but in most countries, the student must have a high school diploma or equivalent (in the United States and Canada, a GED).
Most college students begin their academic careers at 18 years old, the same age when most people graduate from high school. Though, colleges and universities have no maximum age so anyone can study or finish their studies at any time they decide they want.
In the United States and Canada, college students begin as undergraduate students in which they will declare a major in which students specialize in an academic discipline (for example, Psychology, Biology, English, Mathematics, and Economics) and they will take classes that will expose them to the skills they need to do their careers. They also take general education classes which includes courses in reading, research, literature, a math course (for example, College Algebra, Pre-Calculus, or Statistics), a science course, and others (though this will vary by the college).
Upon successful completion of all required courses, students will earn a Bachelor's degree which they may either go to work with the degree or continue studying for a higher-level degree. Students who have a bachelor's degree and choose to continue college are considered graduate students, where they take more classes that are more in-depth to the student's academic discipline and qualify them for higher paying careers, earn a promotion, or become college professors. Students may also attend medical school to become physicians or law school to become lawyers.