This stuff is without a doubt one of my favorite things in the painting world.
Basically, yes, it\'s used to make very thin, semi-transparent colors from regular paints. The advantage of using this stuff rather than plain water to dilute this far is that it maintains some of the acrylic binding\'s strength, so it doesn\'t rub off as easily. Also, it makes it more transparent but still controllable.
There\'s a few topics in the forums here, I\'d suggest you try a search on it. Also, a great article just about using the glaze medium is available over on the Brush Thrall\'s site:
Brush Thralls Glazing Article