Khan Academy has hundreds of videos of every math concept you can
image. They will walk you through how to so things like multiply and
divide fractions, as well as anything else you need to know.
Virtual Nerd is very similar to Khan Academy. They have tons of videos covering all math concepts.
YouTube has thousands of videos where people teach all different math
concepts. Use YouTube only if you can't find what you're looking for on
Khan Academy or Virtual Nerd.