you can inhale and exhale through it or you can just exhale through it. You wait a second after inhaling to exhale. Personally I only exhale through it because it is plastic. But you really can do it either way. I would experiment to see what actually works. I have to do about 16 exhales through it before expelling mucus. And i have to repeat that cycle many times till I feel all the mucus is cleared. Some of those rounds are done lying on my back and sides as well as sitting up. Everyone is different so see what works! I do all this after nebulizing all the saline but again see what works. I tried the Acapella and find the Aerobika more effective.