GATT profiles

Hi Dialog Team ,

Regarding GATT profile could you please help me to understand how the pairing happens and how the services in the profile (health thermometer profile) access the hardware (say thermal sensors) and get the respective value ,which api function does this ?
I understood the basic profiles services and characteristics theoretically ,but still am confused how does these profiles reads the sensor value and where it stores ?
Also suppose if i want to develop a custom profile such that once i paired with my custom board which have a mosfet switch , how can i turn on /off the mosfet by sending a signal to the GPIO pin connected to it ? how do i test this with my USB dongle as client ?

Thanks