In the old days, people had to leave home, travel to a brick-and-mortar campus, and sit in lectures and seminars with several hundred other students. This was expensive and inefficient. Today, tens of thousands can stay home and yet still listen to the lectures online, accessing all the other course materials whenever it's convenient to them.
This gives significant economies of scale. You get to see the best professors yet, because you avoid all the traveling and potential accommodation costs, you spend a fraction the dollars due for traditional education. Better still, to help offset the cost, home-study students can get paid work and fit in study whenever there's free time. This put the student in full control of the speed of study.
This site offers you links to all the best online colleges depending on your chosen area of study. You begin the process by confirming the type of course, the general content and the zip code where you live.
Once this information is supplied, you are moved through to a listing of online colleges where you can compare what's on offer and decide which colleges seem to be offering what you want. With those decisions made, you then get into the detail of courses and enrollment details. This is the most efficient way of exploring what the online colleges can offer you.