External Drive connected to AirportExtreme

After looking around on the web, I am reading that the Airport Extreme can accommodate an external hard drive using its sole USB port.

My question though: Can the data on this drive be accessed only on the local network? I would like to set up my own cloud using this method so that I can access my files on that drive while away from home, either using my MacBook Pro or my iPhone/iPad. If it can, what is the process I would use from those devices to access the files while away from home?

Any thoughts would be appreciated.

Thanks!