There's plenty of places to learn css. This site is one of the many places that taught me. Also look into lynda.com. That method of teaching isn't for everyone but it helped me a lot. Just google css tutorials you'll find quite a few.
W3schools is a great reference but I always find a book is the best way to learn something. I used one called "CSS Mastery" by Andy Budd. It not only tells you the "how", like w3schools, but also the "what" and the "why" (and sometimes even the "why not") with plenty of understandable examples.
http://www.w3schools.com/css/
Have fun!