I am in search for some good sites/site which has some nice notes and explanations about stroke techniques. When I say explanation I mean pictures or something like that to explain whole movement in lets say smash. There are tons of sites with smash "explained" in 3 pictures. Also site where you can exactly read about forearm and wrist techniques and exactly see what is difference about those two. Thank you

Try this site. It has pictures
http://www.asahi-net.or.jp/~zt8s-oon/badmintonshot.htm
or
http://www.sportsid.com/sid2000/default.htm

Also do a search for badminton techniques or get some books

I have not seen any info in books on the importance of the fingers for controlling the racquet. This is an unappreciated area of the game.
I haven't checked out the websites though.

http://www.dynamic.com.my/dynamicwebsite/dynamic_middlefrm_lifestyle_badmin.htm