Arduino with Gen 6 board

Hi,

I have assembled Mendel (3D printer) using Generation 6 electronics board that has ATMega644A incorporated on it.
I need to use an Arduino Uno board to get these two boards to communicate and currently I am a bit baffled by the I2C communication.
Can anyone help me with this. I am pretty new to all this stuff :relaxed:

Cheers,

Javaid