following are some of the useful links to educative videos
http://in.youtube.com/watch?v=ACgPHDzTHaUhttp://in.youtube.com/watch?v=Wi5KSNH2wFk

http://in.youtube.com/watch?v=Q-X-APyRi4E

http://in.youtube.com/watch?v=zKhDvbKrLSA&feature=related