Hi Vicki,
I'm sorry to hear that you are having trouble with your math class. Without knowing more about what topics you are covering in your math class, what kind of homework you have, and what you do when you study for this class, it's little hard for me to say exactly what might help you do better. However, I can make some suggestions that might help.
If you are taking a math class where you need to do a lot of arithmetic (adding, subtracting, multiplication, fractions, etc.) my suggestion is that you put your calculator away and work everything out on a piece of paper. Only use the calculator to check your work when you are finished. I know this probably sounds old fashioned to you, but it really is the only way to learn the basics. At this level, you will probably need to spend a good deal of effort on memorization of things like multiplication tables. The only way to do this is practice, practice, practice.
If you are taking a more advanced class, like algebra or calculus, do not substitute numbers for variables until you are finished simplifying your equations. If you plug the numbers in too early, it is easy to become confused, and if you make an error it will be impossible to find. This is a common mistake students made when I taught physics classes. Working with equations full of variables instead of numbers is intimidating to a lot of people, but it really is easier to find errors in an equation written in terms of variables. I also suggest that when you simplify equations, you write out your work in detail, do one operation at a time and write out the entire equation again after each step. This also makes it easier to find mistakes.
For geometry and trigonometry classes, drawing accurate pictures helps. However, you can't rely solely upon your drawing to give you the answer unless you use a ruler, compass, and protractor to make sure everything is drawn exactly to scale. I hated doing geometric proofs for this reason! Practice helps with these sorts of things, so you should do as many examples as you can. Work through all of the example proofs in your textbook, and only look back at the answers in the book to check your work when you are finished.
In math and physics classes showing that you understand the method, drawing accurate diagrams, and writing out each step in simplifying equations is extremely important. Too many students focus only on getting the right numerical answer at the end, and not on understanding the method used to get the answer. The funny thing is, if you focus on the method and get the wrong number at the end it is a lot easier to go back and correct your errors. If you start a problem knowing the answer is 5, and then just try to manipulate the numbers to get 5, you probably will become very frustrated. Choose the right method, and worry about the numbers later.
Finally, if you have tried all of these things and are still having trouble, don't be afraid to ask adults for help. Asking your teacher or a parent to explain something to you in a different way, or help you find mistakes in your work can be a big help. Maybe your parents can also find a tutor at your school, a local community center, or a library to help you improve your math skills.
Good Luck!
Kris