Highmap on a cube.

I want to use a highmap on every side of a cube. I got the script "HighmapGenerator.js" but that just create a plane.

Or is somewhere a good tutorial for making own meshes with scripts? (I just find crap) Then I could maybe write my own highmap script, but i have to know how to select single vertices and change their position in relation to the old position, and I dont know how to do that acually. I get confused by all the new terms and even did not find exact definitions for all.

Like vertex, vertices, tangents, triangles, normals... =o If I could create a cube like 1,1,1 and subdivide it to have more polys, and then just select the polys i need that would be great. But as I said I cannot find any tutorial that really explains working with meshes.