You don't need a URL, you only need an IP address. (Actually, the internet only runs on numbers, names are merely converted to numbers anyways....). Here's an example of what you currently understand: https://kb.iu.edu/d/aerg
All you need to do is have an FTP server running on either your PC or Android, depending on which way you want to do it. Either works fine and the software/app needed is free. https://play.google.com/store/apps/details?id=com.theolivetree.ftpserver&hl=en
has worked well for me in the past on any of my devices.
All you need to know is your IP address as long as you are on the same WiFI network. Going across your 3g/4g service providers gets a bit more complicated with things like Dynamic DNS and such.