A -- "Excellent work indicating a clear mastery of the subject material." B -- "Good work representing a solid understanding of the subject material." C -- "Adequate work representing significant progress with the subject material." D -- "Marginal work representing barely passable engagement with the subject material." F -- "Inadequate work representing insufficient progress with the subject material."The next step is decide your academic goals for the course. This is sort of important and often over-looked. You might say, "Well I want to get as high a grade as possible," but that's not really helpful. The issue is this: the more time and effort you put into a given course, the higher a grade you are likely to earn all other things being equal. So you need to decide what your priorities are here. Lots of students would like to earn an "A" in a given class. There is no upper limit on the number of students who can earn "A" in Physics 121. All you need to do is demonstrate "mastery" of the material. But this is a step up from "solid competence" that is characteristic of the grade of "B".
Look, you've only got so many hours in a week. And unless you are Einstein himself (and you're not) you need to set priorities. Given your academic objectives, you need to sort our realistically how much time and effort you will have to devote to meeting your goals. Sometimes we fall short of our goals, but having a plan, deciding what is the priority, this will make a difference to how you approach each class you are taking. I am not advocating that every student make Physics 121 a "top priority". I know enough that physics is more important for some students than for others. What I am saying however is that you need to decide as clearly as you can what your academic goals really are and how this class fits in. And then you need to do your level best to arrange your life to meet those goals. That's what we are asking of our students here.