High school and college are different stages of education. You further your study in the college after you might have graduated from high school. So, college is a more advanced level than high school. It is very compulsory, or better said, highly recommended and expected that one should go to high school. However, attending college is voluntary -it's your choice.
In addition, the fees required to pay in high school are very low or even relatively free, while college demands high spending to go through studies successfully. In high school, the student is subjected to the leading or control of parents and teachers. On the other hand, a student in the college will have to take responsibility for his or her life in total, as the lecturers or parents have less control or guidance over him or her anymore. The students in college are usually older than those in high school.
High school and college are two different institutions of education. You can always regard high school education as a type that you need to have before you can proceed to tertiary institution like college. There is a line of similarity between high school and college. High school forms the basis for basic learning processes in students. However, there are a lot of differences between them. High school education in most countries of the world is taken as mandatory for all children, whereas college type of education is optional, you can choose not to further your education. In high school, you are kept in a small classroom with total number of students not more that 35 at most.
But in college, you have a lot of lecture theatres where you can receive lectures with other students. Most students in high school live with their parents, while you can only live in the school environment once you are in college except for some cases when you would to be coming from home, and that makes it to be the sole controller of your time. In college, you deal with advance studies, which means you would need to read more than in your high school days.