I'm trying to do a volumetric light on Cycles, and I've followed tutorials, but nothing has worked yet. How can I make a proper volumetric light in Blender, like the following one?

But to leave the light in the middle, like, almost a star, is this possible? I'm at the point to use an image plane besides the light which would be better... I need to use it moving the camera.
I'm actually trying to do this because I want to simulate the brightness of the Sun.
I tried the effect, but it still gave me an error:







