I got first idea about AVR microcontrollers during my first year summer vacations, in IITK from Robotics Club coordinator Ashwini Shukla. I was really amazed by the power of the microcontroller, a chip which we can program according to our requirements ! Then an era began, me and microcontrollers, Now I cannot live without them :-)
Following are very basic topics for beginners (taken directly from my book),