In the video above we can see the liquify tool in Photoshop being used to draw concept art along with other tools in Photoshop. I attempted to replicate what we see in the video as far as the liquify part.

In this video however the artist selects his deisered color and begins painting out simple blobs of where he wants his objects to be or in this case his rocks and then he changes the colours slighty to different shades and paints over the blobs, bit by bit this method starts to add detail and shading into his image. The artist continues to do this method for each individual object he wants until he is ready to add finer detail. Once he is ready to add finer detail he reduces his brush size and makes multiple strokes with the brush colour set as a white shade of color and the end result of that is visible ridges and slopes in his artwork.

This video may be done by the same artist but first he does his image in black and white and he starts to change he brushes shading much sooner as he highlights the lighting and depth of the image before adding intensive detail. Now he has an impressive detailed black and whit image but he now starts to add color