Whenever a student's grades start dropping, we try to figure out why. Often it's because they don't ASK QUESTIONS when they don't understand something.
Do your best to read the material and understand it. If you still don't understand it, ask questions. After you've asked the question(s), then continue on with your other work until you get the answer. Don't just stop and wait. Often students have an 'AHA!' moment as they are continuing on with their work.
You'll get much better results if you first try to dig out the answer for yourself using the course material, ask good, specific questions, give it your best to understand the answer, and ask specific follow-up questions for anything you still don't understand.
I find that while gathering information to ask my question, assembly my thoughts, then typing out the question, that the answer will finally hit me.
I've started several emails to Instructor Debby that never needed to be sent.