How to go to college after immigrating to America? What steps are needed?

Your situation is complicated, because the United States will not recognize your language school. In their eyes, you haven't graduated from junior high school! You'd better take the GRE or TOEFL first, and prepare like an international student in China. Better get high marks. If there is any specialty, such as Chinese musical instruments, Americans recognize it. I think high school still needs to study. Since you have a green card, apply for a public high school and then go to college. It is unlikely to apply for a lecture. I wish you a happy life abroad.