1. All of the college courses were learned by myself. In other words, I am a self-taught student. (While grammatically correct, it is usually best to avoid starting a sentence with "But". This is especially true if it is the first sentence in a list.) 2. I think this item should be first, but I really don't understand what you are saying. These terms vary a lot by country. In the US, children first go to elementary or primary schools, then they go high school or secondary school, and lastly college or university. There can be a middle school between elementary school and high school. 3. By study alone, I met various difficulties (possibly change to "I faced various challenges"). When I encountered problems, I usually read or thought about these problems over and over again until I arrived at a solution.

I can't read Mandarin , but I will just try to follow as closely as possible to your English translations > Since I have studied all the college courses by myself , I can consider myself as a self-taught student. >Because of poverty, my family decided not to let me go to the high school and then onwards to university, although my grades were good. I only went to secondary school. > Studying on your own can bring about various difficulties , so when I encounter any problem , I will usually think about it a lot in order to solve it.