Sharing harddrive / Airport Extreme

Hey, I have a Airport Extreme which I have connected a harddrive to. I wanna be able to access the harddrive from my iPad and iPhone but at the moment I can only access the harddrive from my MacBook Pro. I have downloaded the Airport tool for iPhone/iPad and I can see find my Airport but I dont see the harddrive.

I would love some input on how I can fix this, so I will be able to access the harddrive from my handhelt devices?

Is it possible to access the harddrive from outside the network like an fttp? (that would be awesome)

Thanks
Oscar M