Hello Gary,
The relevant section of the BT specification you should check is Service Discovery Protocol for an explanation on how UUIDs are used and defined in Bluetooth. They are used to describe particular services and their characteristics - in very basic terms think about it a little bit like port numbers on a PC network, with which you might be more familiar.
UUIDs are 128 bit numbers used to look up attributes but they can be shortened to 32 or 16 bit forms.
Services defined by the Bluetooth standards have UUIDs assigned to them, but you can add your own.
For example, if you want to define a new service, you can allocate your own UUID to represent it. There is a mechanism to minimise the chance of a clash of UUIDs. You can generate a random number for now if you're just testing - you should check the BT standards how to build the correct UUID for an existing service.
Gregg
