Help with studying computer network management?

I recently started a Computer Network Management coarse and need help with studying and retaining info. I took my 1st quiz today and only made a 75. I'm an over achiever and this kind of score will not do. I spend countless hrs reading, but when I took the quiz I didn't recognize many of the question topics. I'm a mom of 4, I work full time, and can't spend that kind of time on one subject. Is there anyone out there that can give me GOOD study tips on studying for this specific coarse. How do I know whats important for me to know and whats not. I want to maintain at least a 3.5 GPA. ANY & ALL RESPONSES WILL BE GREATLY APPRECIATED!!!!! I AM ABSOLUTELY DESPERATE. PLEASE HELP!!!!