This is a site that will allow you to choose different areas of math and find out how things are done.
Fact Monster Math
One more good "how to" site. This site doesn't have a whole lot of relevant topics, but it does have some interesting ones. It also has some games and other interesting information about math.
Homework Helper Problem Solver
This site allows you to type in the problem that you have and it solves it for you.
Interactive math videos of all grade levels and concepts. Includes practice problems.
Released STAAR Test Questions
This has lots of good material in it. The page that I am taking you to gives you a list of classes to choose from that can help you with your homework, from explanation of concepts and examples to practice quizzes.