This is the second throw I learned out of the book–O-Soto-Gari, “major outer reaping.” You get the other guy’s weight all on one foot, the leg that’s “outside,” closest to you, and then you sweep that foot out from under him. The result will be a very gratifying “Thud!”
I don’t think I ever won a judo match with this throw. Everybody knows it, and is on guard against it. But it’s a fun throw to practice.