There's no need to go through the process of getting teaching qualifications in order to teach anymore. If you have a qualification, or a skill - and some good interpersonal skills - there's no reason you can't impart your knowledge or abilities to somebody else. The private tuition industry is booming, especially among adults who want to learn something new but can't spare the time off work to go back to university or college.
Several websites allow you to advertise your services as a private tutor online, including the imaginatively named tutor.com. Whether it's a foreign language or the ability to play the guitar, there will be someone out there who'll want you to supplement what they're leaning elsewhere or teach them from scratch. Depending on what it is you have to teach people, you can charge a lot of money for your time.