Consumer behavior examines how individuals are targeted by marketers and how they make purchasing decisions. It involves three stages: external influences that create product awareness; the decision-making process where psychological factors shape how consumers search for and evaluate options; and post-decision behavior like initial and repeat purchases and evaluations. Marketers seek to understand consumer diversity while also identifying commonalities to effectively promote products through the four P's - product, price, place, and promotion - while consumers are influenced by social and cultural factors like family, class, and subcultures.