I have never had a problem with learning in class, but I do know if I get behind that I can always ask for help. Asking questions in class felt like taboo back in high school. The number of mumbles that you would hear or even the outburst of "you're stupid" was enough to keep anyone from raising their hand. Obvious questions were left unspoken because of the ramifications of looking like you had no common sense (which isn't even common anymore). It began to make me think about the students who were behind further than I am and what they must be going through.
Ask for help.
Getting help with any type of work these days is easier than ever. You have tutors, online tutors, Google, Youtube, Wolfram Alpha, and Quizlet. I personally have these great resources to thank for my success throughout my years of schooling. Utilizing these allows you to not only catch up in class but also get ahead of the ball. Falling behind in class (especially at the collegiate level) can be really stressful because of the other classes that you are taking. You have to compensate for time lost in one class for a time in another and it can easily become a disaster as the semester goes on.
Do not try to be a macho man or woman and fight it out.
If you are struggling with a subject, do not suffer in silence. Suffering in silence is not a good habit and it is also not a good habit to loudly complain about the trouble you are having. To find legitimate help. If you have a friend that has taken a class before you have to take it, go and ask that friend for help. Find your instructor or teacher assistant's office hours. I can't tell you how many times I've gone to see a TA and they are more than excited to help me with my problem. Do you know why they are so eager to help? Because NO ONE ever goes to see them, so they sit in their office all day doing nothing (that's why you always hear someone say TA's doing nothing as an FYI). If you give them nothing they will do nothing.
If you have no other motivation to get help in your class, think about this.
You are paying to be in that class. So, that means you are paying to suffer in silence. Do the right thing for yourself and your pockets and get help!