I need to start over. With my mathematics and science. Any advice?

If you wanna start over...just focus on what you wanna do!!! Math and science are easy as long as you understand the concept!!! Ask questions about things you dont understand!!! I really dont know any websites...but if you get textbooks at school...just type in the textbooks web address and they should give you some worksheets and help!!! Just focus and study and you should do great!! :D