When I was in college, I found a lot of the lessons to be sorely lacking. The professors had a bad habit of relying on Power Point presentations and did little but read the bullet statements out loud expecting you to read between the lines. Unfortunately, this leaves you the student with the responsibility for learning.
So what do you do? For starters, if you have a question about something the professor says, ask questions. Yes, you might feel embarrassed to ask in front of your classmates, but I guarantee you that if you have questions, somebody else in the class does too. If you still can’t bring yourself to raise your hand, go to the professor’s office hours, go to the tutoring center, or ask a friend. Wikipedia is a great source (shh, don’t tell your teachers that Wikipedia has just as valid and up to date information as they do), or Google it. In fact, if you type part of a homework question into Google, somebody else has most likely posted the answer. No, I don’t view this as cheating-the point is to learn, not spend hours and days trying to figure something out.
To that end, whenever I found a useful tidbit or explanation, I wrote it down. After a while, I needed a way to organize all my notes, so I started a forum to share information. Please feel free to browse and I encourage you to join and contribute what you can.