Some of you already know about how it's a little pitcher that you fill with lukewarm salt water (any kind of salt - just no iodine or additives). You just poke the spout attractively into one of your nostrils, lean over the sink, sort of downward and sideways, and pour the solution in so that it drips right out through the OTHER nostril. Presto! Like being able to wash out the inside of your head!
There are lots of easy to find YouTube videos that explain and demonstrate this better than I can. But aside from making you (you with a cold, that is) feel instantly MUCH better, it can prevent the cold from becoming a sinus infection. Also it can be important to use when you think your immune system has been compromised, such as having been on a plane, or a crowded subway in flu season, or in a room full of people sneezing. It washes those nasty germs right out before they can "take hold"!
I got a really ugly plastic one from CVS. You can get artful ceramic ones. Or official Himalayan ones. Or one of the videos I watched shows a kid just using a funnel - once you get the idea that you just need a way to channel salt water through your sinus cavity you can pretty much do as you please.
I'm happy to have learned a new trick, and the cold is pretty much history now.