Is there a folder system viewable by applications is there a folder system view able by application android, i.e. if i put a music file for example in it, I can see it from the music app??

I have android 5 on a tablet.
A music application will look in certain places for MP3 (or other format) music files, and show them in whatever graphical browser the application has built in. 

Conversely, a file manager will show you the file and folder structure of your Android system (well, as much as is allowed by root/non-root permissions).