Embedded Labs has come out with a very detailed I2C 101 tutorial, that you should check out if you have any questions on the system. I2C is a short distance serial interface that only requires 2 bus lines. Keep in mind that as wires go down complexity goes up. While there are more than a few I2C devices out there in the wild, and the 2 wire system does make wiring a breeze sometimes, the information required to make use of it often seems confusing to someone who is just starting with it.
The tutorial covers basic theory, stop / start conditions, addressing, data transfer, and acknowledgment plus illustrations. A couple of specific examples are given in the form of a 24LC512 serial eeprom, and a DS1631 digital thermometer complete with code.