what is the difference between and instructor and a professor?
The term professor has two meanings. The word professor can either refer to a teacher in a university or a college or the highest ranking position of a university. The main difference between teacher and professor is that professors work in a tertiary education institute.
The answer depends a lot on what country and what institution you're referring to. So there's no single answer. In the US, an instructor (also sometimes called a lecturer) is someone, often without a PhD, whose only job is to teach (part-time or full-time).