How do credit hours work and what's the difference between part-time and full-time?

I don't understand how credit hours work. Part-time I think is 12 credit hours a semester and full-time is 15 credit hours. If I went part time does that mean that I have to get 12 hours a week?|||What I am about to tell you is true for MOST but NOT ALL schools. A regular class like math, english, ect is worth 3 credit hours. A science class with a lab is worth 4 credit hours. At most schools 12 credit hours a week or more is full time and 11 credit hours or less is part time. So you would need to take about 4-5 classes to be full time.