VERY SIMPLE !
Open the app on your phone, it will link to another device (via WiFi) by entering the browser URL displayed on the phone, on your PC, laptop, tablet (et al) browser. This exposes the phone storage to the other device & it's transferred using your existing WiFi connection (operative term WiFi). Goes both ways (phone to device & vice versa).
I believe being on a WiFi network is a requirement !
But when that page open in other phone,ican only play the music/videos. Bt how it download/upload?