I've been getting bad grades on tests lately. Right now I have a C :( my sister says math is really important and u should do good on it. I really really try and understand the lessons but I can't. Is there any extra online math websites classes I could look at to help me? I'm in the second highest math course/class(3/4)

You really need a tutor if you can... to find and focus on your weakest parts of math.

Something an online course can't really do too well.

Your sister is right... Math is a very important subject.

Have you talked to your teacher? Sometimes they will meet with you before or after school to provide extra help. Is your sister or a parent able to work with you on it? Have any friends who are good in math who would help?

As smoothy said, find out about getting a tutor to help you understand the different concepts better. Having someone in person to explain things will be more helpful than online. Sometimes having the information presented in a slightly different way will help you to understand it better. Ask a few people and you'll likely find someone who would be happy to help.

I suggest looking for a online course and asking for help in class and getting help before and after school.