The word 'self-study' is rather self explanatory. There really isn't any fixed way to studying a topic on your own, except that you have to be persistent, disciplined and very interested in the topic itself. Interest should be the main motivation behind self study. If so you need no recognition from colleges because you have already derived a strong sense of accomplishment from learning a subject by yourself.
In the long run, you have to do self study to continuously improve yourself. Learning should not stop at school or else it defeats the purpose of study. Schooling merely teaches you the way to study, the approach and attitude you should adopt towards study. Many of the subjects you learn in high school will never be used in your life; the purpose of studying those syllabus is to find your way to study for each type of subject (like different approaches to studying literature and maths).