This guy is absolutely tremendous. I got turned on to his videos several months ago quite inadvertently through a series he did about astrophysics, but shortly afterward discovered that there is an enormous body of instructional material on his website and excellent YouTube channel. Sal Khan is the maths/science teacher you wished you’d had in high school or college!
Also, and this is by no means intended to be dismissive, but if you happen to have trouble sleeping at night, just tune into a playlist of lectures about solving quadratic equations, or whatever… Works like a charm. And, if you subscribe to the notion of Hypnopaedia, hey, you may even learn something that way too!