Lessons In Electric Circuits by Tony R. Kuphaldt, et. al.
Rather than try to teach you what you need to know about electric circuits on this site (an effort I started but lacked the time/will to continue) I'd like to refer you to a very comprehensive online text book I discovered hosted over at iBiblio.
This book reminds me very much of the books I used to learn electronics at a vocational college course back when it was worth the effort to fix a circuit board rather than throw it away and get a new one. Those books and courses have served me extremely well in my robot experiments. It may seem like a ton of stuff, and it is, but you can work your way through it over time. If you do work your way through it you'll have a great foundation from which to continue you robotics experiments as well as expand your understanding of electronics.
You should also hit the website: http://www.allaboutcircuits.com/ which is dedicated to these books and even has forums about them.
Since the book is copylefted I have downloaded and linked PDF versions of each volume here: