Math Tutorial Website?

Okay well I did well in 11th grade math, however I'm doing 12th grade math now, seems like my old teacher didn't teach me some things I need now... I'm at a different school now, in a different region so I can't go back to him and ask, and my current teacher is a bit of an ******... There's no talking to him. I want to teach myself some of the topics needed, I'm currently doing modulus & Inequalities Quadratics, but I still dont completely understand the foundation of quadratics and other topics that weren't taught fully. Can anyone suggest a FREE website they used to teach or help them brush up on any math problems they had?