I could've lived another 100 years and would probably never realize on my own this is possible. I've previously inhaled sea water with my nose to force being able to equalize when having problems doing so due mucus and/or inflammation of the Eustachian tubes. But this flushing is so much more pleasant (after you get the hang of it) and more hygienic. I feel really clean and breathing easier after doing it. I can't tell you specifically what it cures, there's information about this online. I use it as needed, sometimes after a task that I felt put some unhealthy stuff up my nose. Certainly after a day of diving.
My neti pot is the cheap $5 one from Walgreens. There are different style ones, they're all basically like a little tea kettle without sharp edges that would hurt your nose. I'd like to upgrade to ceramic pot just for the hell of it, but it's more likely to break and the plastic one works fine. I use my filtered drinking water, heat 16 seconds in the microwave to get the water a little warm, and mix in the salt with a finger. At this point I'm familiar with the sensation and angle I have to tilt my head, I can get a nice stream going like the girl in the vid just not as easy on the eyes
How to perform nasal cleaning with Neti Pot by Advaita - YouTube