What will I learn in a literature and composition degree or training program?
A degree or training program in literature and composition is really trying to teach you the same thing in two different ways. To organize your thoughts and express them clearly is the basic idea, to be able to explain using the written word both what you mean and what is going on in a particular scenario. The literature part is really showing you how the great writers of the past and the present do so. Composition is trying to teach you the tricks of the trade, the techniques which experience has shown us work. This is much more than simply grammar and spelling, it's the art (or science if you prefer) of explaining an idea, a story or an emotion clearly and in a compelling manner.
What will a literature and composition degree or training program qualify me to do?
What won't it help you do is rather more the question. The ability to explain things in simple and compelling language, as anyone who has ever read a corporate report will know, is sadly all too rare. A full degree would be a good base for graduate training at business, law, or journalism schools while a shorter training program will be of value to almost any future career. Even if you decide against writing as a career, there is almost no job that does not require reports to be written: knowing how to write them will be a boost to any career.