There is usually a state test you need to take in whatever area of specialty you want to teach. Some schools prefer you to have a teaching background so you may need to enroll in some teaching courses in college. But as far as just getting your license you just need to prove (by taking the test) that you are knowledgeable in the subject area.
The requirements vary widely from state to state. The first step is to head to the web site for the Department of Education for your state. The requirements for teacher credentialing will be listed there. Most states require a certain number of university courses in education, one or more tests, and possibly student teaching. Begin at the web site and go from there and hopefully you are not from California!