An instructor is a teacher. One can be an instructor of just about anything, but it usually applies to teaching hands-on skills, like a water-skiing instructor or the instructor of the knitting class held at the community center.
When you instruct, or teach, other people how to do something, you are their instructor. At a college, you might hear some of the people who teach classes referred to as instructors and others as professors. An instructor might teach only part-time, or be a graduate student, or, for the moment at least, not be on the path to receiving the title of professor. Still, instructors are teachers: they have their own classes and students.