You are getting right to the "meat" of things. Questions are fabulous - ask them as they come to you!

I'll try to give you a basic explanation, if you want to read more just Google it. Postural drainage is the process of using gravity, with or without manual percussion (thumping/clapping) to encourage mucus to move from deep in the lungs, up through the airways where it can be coughed up. It was originally used for Cystic Fibrosis, but has been found to work with Bronchiectasis, COPD, even pneumonia. It is generally used immediately following the neb to be most effective.

Here is a slide show showing positions https://www.slideshare.net/Rv_252/postural-drainage-116651539 It is good to know which parts of your lungs are most affected so you can focus your efforts. For example, I am in the midst of an exacerbation (flare up) in my lower lobes, so once a day, after I neb, I do the hips-up posture for a few minutes to get the junk up. My upper lobes clear easily with the neb & coughing.

If you do not have someone to do the "thumping", you can use a vibratory airway clearance device (Aerobika and Acapella are most common - Google them)

If you think you need to use postural drainage to clear your lungs, it would be best to have a couple training sessions with a Respiratory Therapist to get the positions and techniques just right for you.

Keep reading, and keep asking -
Sue