The most obvious difference is how long you will study at the college for. Two-year courses last for two years and four-year courses last for four years. This does lead to some major differences. Four-year colleges are more expensive, so the student leaves with more debt, but on the other hand, four-year courses tend to lead to better jobs.
Starting salary is a major concern for students going to college. Two-year-course students tend to start on a lower salary than four-year students, but this has much more to do with the courses available at each institution than any form of discrimination.
Two-year degrees are much more technical or vocational than four-year versions, which tend to deal more with academics. Certain career paths, such as the law, require four-year schools but result in higher pay. Associate's degrees from two-year colleges are for much more practical subjects, so it is a question of what you want to study, not how long you want to study for.
Two-year colleges have been seen as a lesser form of education than four-year equivalents, but this attitude is not true at all. The difference lies in what is taught, not in the quality of education received.