The mouse is here. Gave up on looking on the web for programming help and ordered a book on the Raspberry Pi. While waiting for this to come thought I’d look at the GPIO bus.
The GPIO bus allows the Raspberry Pi to control external electronics and handle various inputs. As well as 17 Input and Output pins, it also provides a 3.3V and 5V supply. Looking on the web, found this site which has a lot of useful information on the GPIO bus and explained it very simply.
One concern seemed to be that these pins are not protected in any way. the pins go stright from the GPIO header into the pins of the IC without any type of protection. In my experience, and GPIO bus where it is controlling external electronics various voltages can be connected by accident and cause permanent damage to the IC. For example an input that goes well over the expected voltage can result in an input pin being pulled high, say well above the supply voltage. Reverse connection of voltage are also a possibility.