Selecting polygons and defining shading domains is only one step of the process,.
Shading domains tell the program which part of your model get applied with the shaders you’ve made (you’ll normally need to create shaders after you’ve defined the “shading domain” area’s, and then apply your new shaders to those parts,. before you can actually see the textures on the model.
You need to tell the program “How” to “project” the 2D images (from your shaders or texture maps) onto the 3D surface of the model.
that’s called UV Mapping,. and all object need to have some form of basic UV, to allow textures to be applied correctly.
You select, define, or change the UV Mapping, for the entire the model, or individual shading domains. in the Vertex Modeller.
for example : Box UV mapping,. will project the texture map from the top, left, right, front, back, and bottom of the object so that the 2D texture is applied to all parts of the 3D mesh.
UV Unwrapping, or pelf mapping uses a process where you define a seam, (or several seams and pins) like a tailor cutting seams on a cloth pattern,. and the program flattens the 3D model out,. into a 2D UV grid area,. where you can then choose to export that layout as a texturing template (black and white wire-frame)
The shader you’ve posted,.. (the “bricks” shader) is a “procedural” shader,. rather than an image of bricks,. this allows you to change the values of the procedural shader, to create different sizes or quantities of the brick pattern.
at the moment,. it’ll be white bricks with black mortar,. but you can create a better effect by using the Bricks pattern as the Blender for two different colours in a mixer shader. (pic)
Procedural shaders also use the objects UV mapping,. but you can also bypass that, and use a basic “forced” mapping from within the shaders.
here’s some pages which may help you,...
hope it helps
Click thumbnail to see full-size image