Boni, the U & V coordinate nodes are read-only; they have no inputs to show, and the little preview window will only show a linear gradient (left-right for U, up-down for V). They output the UV map coordinates. By connecting them into the Tile node's U & V offsets, you can rotate the tiling so that it runs diagonally. (You could also flip/mirror). The Cloud node has inputs and numeric adjustments, and its mini preview window is useful. Looks like Sam is giving the metal some surface variation with the Cloud->Blender chain.

Having just a numeric value in a "value" socket applies a constant value all over the material zone.

You can have that value vary by mapping the changes (use an image map or movie node as a mask, or use one of the texture nodes such as Tile).

You can apply a 3D texture node which will apply to the geometry even without UV mapping (Cloud, Spots, Cellular, Turbulence, Noise, etc.)

You can vary the value by math/geometry variables (frame number, N, P, u, v, dPdu & dpdv, etc.) - These can do things like react to edges/corners (wear scuffing on a metal crate), or apply only to topside horizontal surfaces (snow on rooftop)

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5