Quote - Okay, then, something I saw recently in a video got lost in translation about sculpting. I actually thought it made things smaller and subdivided vertices and polygons.

The model only "shrinks" if you have a smoothing modifier on it. The shrinkage is caused by the smoothing. If the smooth modifier is not on then it will only increase the poly and vertex count of the model.

A vertex can't be subdivided. It's only a point in space. The edges that connect between two vertices are divided in equal lengths by a new vertex. So if you have a single quad face, that is 4 vertices connected together by 4 edges. One subdivision level will add a new vertex to each edge and connect a 9th vertex in the center point, giving you 4 faces from the previous 1 face.