A UV Sphere is a better mesh to try this on (is made out of quads, and not trianlges like the Ico Sphere). 

You need to plug the displacement texture to the displacement node.

Render Feature set has to be in Experimental.

Displacement has to be set to True or both.

To preview, you have to be in Rendered mode in the viewport. Other Shading modes will not reflect the displacement, and it does not refresh in real time. You have to exit Rendered mode and re-enter to update.

The more subdivisions you have on your mesh, the more detailed the displacement, but it will also have an impact on the performance of your computer.


Remember that is still an "experimental" feature.




[![enter image description here][1]][1]

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/uCpQX.png
  [2]: https://i.sstatic.net/BrlaX.jpg