As the name suggest, polygonal modeling involves constructing the models out of polygons. Strictly, software packages works only with triangles. Blender could show you quads and some software packages could even let you work with polygons with more than 4 sides (n-gons) but these packages work internally only with triangles. These triangles are hidden so that you could concentrate more on modeling.
While different modelers works differently, they would still follow certain workflows (some call this techniques). These are familiarly called box modeling and polygon-by-polygon modeling (poly-by-poly modeling).
Box modeling is a top-down approach where modelers start with a primitive (usually a cube (box), hence the box in box modeling). Then from this primitive, the model's form is build up where details are gradually added.
Poly-by-poly modeling is almost the opposite of box modeling. It is the bottom-up approach where modelers start with a plane or even a vertex. Using extrusion and other tools, more geometries are added. Polygon by polygon the model is gradually build.
None of the two is better than the other but there are instances where one workflow lends much better to the situation. One typical advantage of box modeling is that at early stage, you are able to conceive first the form (the whole) of the model and is better equipped to do general corrections without bothering yet with the details. Poly-by-poly otherwise give you more control on the geometry and is much more easier to use in modeling complex forms like the human ear. Complications do arise when working with the two. In box modeling, it is typically difficult to manage the geometry when adding details. Experience is necessary so as not to create a mess. Poly-by-poly modeling otherwise has its own quirks. Since you are going detail by detail, it is easy to make a mess with the models form (i.e. wrong proportions).
While the two are opposites, they compliment each other beautifully. Most modelers would combine the two workflows in a variety of proportions, combining the strength of each. For example one might model a human body using box modeling while the head and the ears are done using poly-by-poly modeling.
Blocking with primitives is added to enrich approaches is modeling. It is basically box modeling in conjunction with divide-and-conquer approach. Different parts are modeled separately with their own primitives and later attached with the others to form the whole.