I've taken a few online classes before. One I took was biostatistics and I had kind of a bad experience with that one. The professor didn't make powerpoint slides up for us to learn from. She would just tell us to read the examples in the book and learn from those, and by the way the book was horrible at explaining things so I had a rough semester.
Our online classes used WebCT to host them I don't know if most use WebCT. Most of the time the professors would send out reminders of when homework was going to be due, or when we needed to have our test turned in by. That showed up as an "announcement" on WebCT. Most of the other online classes that I had provided some kind of powerpoint presentations with audio that you could listen to.
The thing I liked about online classes is that if you have a job or other things, then you can watch them whenever it is convenient for you. So if you wanted to watch it at 2am in the morning, then you could do that, it is your choice.
Your assignments are basically just attached/uploaded through WebCT and then uploaded onto it for the professor to grade. You could also view your grades through WebCT and take quizes through it and even your tests. We weren't supposed to have open book tests but when you're taking the test at home then it's kind of hard not to want to look in a book for the answer if you don't know it off the top of your head! I know, I was bad sometimes. You have to be willing and disciplined enough to watch the lectures though online. I know sometimes I wouldn't even listen to the audio, I would just glance through the powerpoints myself since it was quicker, but that way you miss important things that the professor might have said.