Yes, you need something called a USB OTG cable which will allow you to hook up external USB devices such as flash drives, hard drives, mice / keyboards, etc...
You also need to either root your device or install something like Nexus Media Importer (from the Play store) which will enable the USB port for reading/writing.
Also, you can't necessarily read external drives which pull too much power - like USB powered hard disks. But it will do USB flash devices quite nicely.
Alan
My question is' can I access an external drive via USB
I've found the Nexus can't supply enough power to the drive, so I ended up buying a USB Y Cable to supply power and it works fine. I installed the Nexus Media Importer app.
Where do you plug the "Y" end of this cable into? The single end goes into the external hard drive. The Nexus only has 1 micro-USB slot, right?
Thanks,