can i use my amd radeon r7 265 with cycles opencl rendering in blender 2.78 b . and how to enable it ??? help me please
The AMD radeon r7 265 is on the list of supported devices: https://wiki.blender.org/index.php/OpenCL
There are two settings you need to change to enable GPU rendering. The first is in User Preferences like you show, and the second is in the rendering tab of the properties panel.
Increase tile size for better GPU performance with non-progressive rendering.