The Warp shader is used to displace texture, be that a fractal, image, or simple shape shader. Anything that lives in texture space (which includes clouds).
You need to drive the warper input with something that gives you directional displacement, which is either a Redirect Shader (which needs a displacement in one of the x,y,z inputs) or Vector Displacement Shader (which only requires a value in x,y,z).
This is quite a powerfull tool. You can use it to 'sex' up bitmap textures by 'warping' them, so that as you get close to seeing the pixel blurring as you get closer to the texture, you can add further interest/resolution by adding noise to the now large pixel edges. (I'm not sure this makes much sense. Think planet or satelite photographs as ground textures.)