Jala neti is originally a yoga tool. However, you don’t have to be a yogi to try it. It’s a simple kettle into which you pour water, insert it into one nostril, and let the water flow out through the other nostril.
For me, the main benefit is clearing the airways. After using it, breathing becomes much easier. It’s also good to add a little salt to the water, otherwise it can be a very unpleasant experience, similar to getting water up your nose while swimming.