We have been given a living room set, a bedroom suite, hundreds of Legos, bushels of tomatoes, a bed mattress and more. Yes, free things can be good!
Sal Khan explains things to students. Not saying that they always understand him either, but they can listen to him repeatedly without him getting frustrated with them. That's a super good thing. He always says the same thing in the same tone of voice... because it's on video.
One does not need to repeat 80 percent of the material here, as often happens in a classroom setting, because things are taught on a mastery basis at Khan Academy. Once you've mastered a concept, you can move on to something else. It is a myth that you need to practice and practice and practice to be able to understand math concepts.
Yes, some practice is needed but once you understand it, you understand it. More practice is not needed. And practice will not help you if your brain is not ready for a concept. It will only be frustrating. Cognitive readiness is a huge factor when learning math.
"Conveyor belt" schooling puts all children the same age, in the same grade, doing the same things. Then it labels them slow, average or quick. Our children are humans, not machines and just because one child is cognitively ready to learn addition at 3 (or 6) years of age does not mean that all children are.
Math is meant to be explored and enjoyed; but with the way it is taught in schools, it becomes one of the most hated subjects out there. This is so sad because math can help us understand more about our orderly Creator. Khan Academy gives you the chance to take math at your own pace, in your own time, and be okay with who you are.
After you've signed up at Khan Academy, look for the drop-down menu on the left, labeled Subjects. Under the Math by subject tab, find Arithmetic. That is the best place to start, in my opinion, because it will help you fill in any "holes" in your math education. I enjoy continuing my education here.
Here are screenshots from my phone to show you how much is under the Math by subject heading.
Listen to Sal Khan explain things more at a TED talk.