how do i access a USB drive on airport express

An express cannot use a hard disk.. only the extreme or time capsule.

I am not sure what you mean by iTV.. an apple TV must work with iTunes.. so you need to use a computer if you have iTunes library on the hard disk. Then mount the disk in iTunes to see the library and the Apple TV can then use it.

A normal smart TV cannot use any apple airport as a media store.. the airport routers have no media extensions.

A WD live TV can use a hard disk plugged into an Extreme for example.. because it is a proper media player. But the smart TV needs DLNA protocol support.. which Apple does not use.

There must be a computer in the network running iTunes.. it will not work without. Apple built all their media around iTunes and there is no iTunes built into an apple router.

Which exact model of the AirPort Extreme do you have?

As LaPastenague has pointed out, the Apple TV is not an iTunes server. It cannot be used to pull media files from a network drive, like an AirPort Disk connected to an AirPort Extreme, for the purpose of streaming.

You would either need to run iTunes on a Mac or PC or a dedicated iTunes server to do so.

So is the issue not being able to stream from a Mac connected to the media files on the AirPort Disk or connecting either the Mac or the Apple TV to the Extreme's Wi-Fi network?