Android Phone USB port

To real geeks, this will seem like a stupid question but I need s definitive answer if anyone has it!

I was in a phone shop in Cambodia and a clerk plugged his UUSB flash drive into my phone. I want to know if this can be done with all flash drives and any phone? I have just bought a new Samsung Grand and would like the convenience?

Part 2
The same question but with an external hard drive. Is there an adroid prog that can substitute for windows to allow my android devices to read my externals?

Part 3

I bought a USB Bluetooth device for my Win 7 notebook but it does not get picked up. I tried downloading generic drivers but without success. The device package claimed Win 7 & 8, so I did not expect a driver to be needed. Any suggestion of how to troubleshoot this device I bought?

No one out there able to help. I spent a LOT of time on this issue as it would be very convenient. Sadly, my conclusion alienates me further from Samsung product:

I asked guru at a phone shop at Pantip about connecting and showed him using my adapter cable and my USB. He spent close to an hour trying to troubleshoot. He put my cable and usb into his UNrooted Sony android which read all the files without hesitation and then did the same with his Windows PC. He then tried the Samsung phone of the other staff and it would not read at all. He then took a 500 baht flash drive intended for smartphones specifically for this very task with the large and micro connector on either end. It read on the Sony and not on either of the Samsungs. He then went to another shop and borrowed a specialty adapter cable but same result. Finally gave up. So Samsung has either screwed up their android version or are purposely blocking USB devices being attached.

It also means that it was highly unlikely the 600 baht Samsung adapter cable that the Samsung shop tried to sell me with their assurance that it would allow my phone to read the flash drive, was correct. Of course they would not guarantee it by giving me my money back or opening the package to prove it would work.

The dongle you're seeking is used with devices compatible with USB-On-The-Go or abbreviated to USB OTG Paul.  Not all phone are USB OTG compatible.  Ask a mobile phone shop for a USB-On-The-Go dongle or show them a picture of what you want.  I think they shouldn't cost more than 200-300 baht.

FYI:  USB OTG isn't just for USB drives either.  I have used a USB OTG dongle to plug a keyboard into my Samsung Galaxy S3 and used it to type emails with.  

  

Many thanks for your reply Mike.

Unfortunately, I don't think it resolves anything. I have bought a half dozen OTG adapter cables of two models, one of which is shown in your attached photo. A phone shop at Pantip tried 3 additional models of cable, none of which worked on either of the two Samsung models I have. The Samsung Service Centre Manager tried my two cables on both of my phones with no success (and yet they worked on his Gslaxy Grand with newer software not available for my slightly older Grand 2!) plus he brought in a new Kingston OTG memory stick which again would not work on either of my phones but did on his.