I2C is a bus for communication with devices like LCD...
MCU = microcontroller ~ like ATmega328P on Arduino UNO
Yes you can use as I/O (SDA, SCL) but they are the same as A4,A5.
As Robin wrote, any of pins 0-13 and A0-A5 can be used as digital I/O. Pins like AREF, IOREF... have different purpose.