It works. Worth taking for a short term reduction in water retnetion. I don't recommend using it (or ANY diuretic) longer term. Works very well for that "special event" or for period-related water retention.
If you have an ongoing problem with water retention, try lowering salt intake and/or increasing water intake.
Just follow what is on the bottle. Usually it is one pill 2-3x a day. I think this usually gets you in the 1g (1000mg) a day area, but can depend on the brand.
Just make VERY sure you keep drink water while taking. In fact, drink MORE.