by Chris Tyler:
Some polygon editing basics for beginners, Part 1
This polygon modeling tutorial is designed for people new to polygon modeling who want to better understand the nature of geometry construction. It covers the nature of polygons (triangles, quads, ngons) and their subcomponents (vertices, edges, fill), overlapping vs connected elements and possible problems that can be encountered when constructing geometry. It also shows how to use active grids to carefully construct geometry.