You can go over some books recommended by a few good programs. First you should have some math background including deterministic and stochastic models, and some statistics. Finance has a lot of branches which have different requirement for qualification. You need to know what your plan is, step by step after an overview.
Another way: You should have common sense in finance if you have a transaction in your major. Reading wall street journal and financial times can help build this common sense. Anyway, it is actually not easy for man to transfer his original major to this fields and you need work harder to achieve more.