How do I navigate to program files and programs on PR4100

My Cloud OS 3 Personal & Network Attached Storage My Cloud Pro Series
4

Your question is vague… which application directory are you looking for?
I thought you meant this:

I installed the Plex application on my PR4100 via the web interface.
Where to find the application directory and configuration?

In that case you’ll find all you need in /shares/Volume_1/Nas_Prog over SSH.