Basically it is adding more salt than normal to the water nasal solution (making it more saline, like ocean water). The idea is that the higher salt content exceeds that of the normal mucus in the nose and draws the moisture from the inflamed sinuses and causes them to be less inflamed--sort of dries them out.
For me, I'm using 3 of the packets you can buy at the drugstore for your Neti pot or nasal wash device. Normally you just use one.