How does this USB app work On IPhone

I do not understand you question. What USB app? How am I supposed to know?

Wy don't you ask the app developr

this is a user helping user forum

ios have more then a few apps available

so spc app questions will get more productive replys

in the forums for the developer or app in question

It allows you to store various documents on your phone. You must use iTunes to transfer the documents. It does not turn your phone into a "USB Stick", if that's what you were thinking.