I assambled rear wheel hub, but now rear wheel is not turning freely I disassambled/assambled rear wheel hub, but now rear wheel is not turning freely, what have i done wrong?
You likely tightened the cones too tight.  Read up on the proper procedure for cone adjustment and be sure to grease it up well.

http://sheldonbrown.com/cone-adjustment.html

OR 

http://www.parktool.com/blog/repair-help/hub-overhaul-and-adjustment