Hi Johnsonchan,
First of all Beekit is not a codegeneration tool, but a project developmet/configuration tool.
It can not generate code on how to "sample a gpio pin" and sent it over the air.
To learn about how to access the GPIO pins you must look at the reference manual and example code for the CPU on the EVB board. the CPU is a HCS08 GT/GB 60 and you can find datasheets, reference manuals etc on the 8 bit microcontroller page:
Here is an example of a few macro's that can be used to set a port pin:
#define ExternalDeviceInit() PTBDD |= 0x40;
#define ExternalDeviceOn() PTBD|=0x40
#define ExternalDeviceOff() PTBD&=~0x40
#define ExternalDeviceToggle() PTBD^=0x40
To learn how to develop a ZigBee applicaion i would suggest that you read the documentation that is included in the Beekit:
First read the ZigBee Application user's guide and do all the instructions in order to learn how to use the demo application.
Second, read the Beestack application developer's guide and do all the instructions in order to learn how to develop a custom ZigBee application.
BR,
Mads