Drop down a volume node to insert a VDB volume into a Solaris's scene and select the desired VDB file. 
In the example above, a variety of cloud VDBs was used.  Smaller cloud VDBs were placed in and around the two open TeaPot flight cases and a large dense cloud was placed in the center of the scene.

A PxrVolume material was created and the density was controlled via a PxrPrimVar node 
Note : If you find your density is too dense, you can control it further by using a PxrExposure node and reducing the exposure to lessen the density of the volume.

In the example above, a small layer of fog has been created to add a touch of air volumetrics to the scene.

To achieve this, a sopcreate node was inserted,ed and within that the following setup was created.  The density is controlled inside of the volumevop node