1) The document discusses different types of unit cell structures in crystalline solids, including simple cubic, body centered cubic, and face centered cubic unit cells. 2) It also describes the packing efficiency of each unit cell structure, with face centered cubic being the most efficient with 74% of space occupied by particles. 3) The document outlines the three stages of packing - linear packing in one dimension, planar packing arrangements, and three-dimensional packing. It provides examples of AAAA and ABAB planar arrangements and how they correspond to simple cubic and hexagonal close packed 3D structures.