I2C is a bus that allows you to communicate small processors and boards. You will find lots of information in the links taht Richard has posted.
Knowing that I2C is a bus (see
this[
^] Wikipedia article) will help you to understand it better.
Get the manuals of the devices you want to communicate.
I've seen that to control small motors and drives from a small board for an autonomous robot and in each single case the I2C specs are always there. Keep in mind that nobody will manufacture a device without giving you the information to communicate (making it work) with it. Read the manuals!
Good luck! :thumbsup: