It's essentially a gravy boat-teapot hybrid made out of white ceramic (dishwasher safe!). On one end, a little handle, and on the other, a pointy spout that you stick in your nostril.
What you do is you mix up a little tap water & salt mixture for pouring through your sinuses. The pamphlet that came with it didn't exactly recommend iodized salt, but it's all we have, so it is what I've been using. I have found that the temperature of the water is highly important. Too cold, and it's shocking; too hot, and it irritates the back passages of my nose. I also don't put too much salt, because I think that adds to the irritation, and that's not the point.
What the salt and lukewarm water mixture is supposed to do is gently buffer up the mucus lying in wait back there and wash it out. Salt water is my new favorite remedy for everything. It's not only good for this purpose of flushing out your sinuses, but it also heals piercings, loosens coral out of scrapes in your knee, and cleans and heals bloody scrapes.
I'm pretty much a believer in the neti pot. It hasn't completely gotten rid of my allergies, whatever they are, as the testimonials on the box claimed it might. But I watch in the mirror as I'm pouring water through one nostril and out the other, and big globs of whitish mucus always come out in the stream. When I have run the water through once or twice each way, I can feel the air coming in through both nostrils. My sneezing is calmed for at least a little while, until the pet dander, vog, dust, and pollen have a chance to build up in there again.
I would recommend the neti pot to anybody with allergies who has an aversion to drugs and all things non-natural, like I do. But I would NOT recommend it to anyone closed-minded or who is afraid of uncomfortable sensations. This is because I think a large part of its healing depends on the individual's belief that it will help; you cannot compare it to prescription allergy medications. Also, it feels a bit like jumping into a pool without plugging your nose. My eyes water a little, and my sinuses sting ever so slightly. The most uncomfortable part is before the water starts draining through, and it is making its way past the threshold to where it comes out the other side.
I feel good about using it, though, and cleaner for it. You can blow into a paper tissue all you want, but that doesn't get back into the deepest recesses of mucus land. Also, the neti pot method leaves no tangible waste, just muck that washes down the drain. It is the green, natural alternative to standard allergy solutions.