Hi,
What is the use of the ADC port given on the microcontroller atmega 16?
The A/D-C (Analog to Digital Converter) is for converting analog voltages from eg. a sensor into a digital value.
With a 10 bit A/D-C ans a reference voltage of 5V, an analog voltage will be quntitized into steps of roughly 5mV (4.883mV).
how can it be used??
If you're after the exact code fror using it, take a look at the software board, Google something like "ATmega16 ADC code", or try
this tutorial.