Raspberry Pi i/p pins are located in the upper left corner of board, see following picture:

These pins are combination of Voltage supplies, Grounds and GPIO (general purpose input/output) pins. You can distinguish them from following graph:

Understand those pins functions are fundamental to design projects which allow Raspberry Pi to communicate with sensors and many other devices.

Detail explanation of pins:

if you want to write code to test GPIO code, check our tutorial Use LED to test GPIO pin