1 credit = 1 hour of class / week. As an international student you must enroll for at least 12 credits, which would mean that you would have 12 hours of instruction / week.
It may seem light, but remember that in the U.S. you have to do a lot of homework, such as reading, worksheets, papers, and research. Therefore, you will have as much work as what you may have now in your country.