Lipids are essential biomolecules that play critical roles in energy metabolism, cellular structure, and physiological regulation. This review provides a comprehensive overview of lipid metabolism and membrane structure, highlighting the biochemical and functional significance of lipids in the human body. It begins with the classification and importance of lipids, emphasizing their roles in energy storage, insulation, protection, and cell signaling. The structural and functional diversity of fatty acids, including saturated, unsaturated, essential, and non-essential types, is discussed in relation to their metabolic and physiological relevance. The review further explores triglycerides as the primary storage form of lipids, detailing their structure, classification, and metabolic pathways. Key processes in lipid metabolism, including digestion, transport via lipoproteins, and storage in adipose tissue, are discussed. Particular emphasis is placed on the degradation of fatty acids through β-oxidation, including activation, mitochondrial transport via the carnitine shuttle, and energy yield, as well as the unique metabolism of odd-chain fatty acids. Lipolysis and the metabolic fate of its products free fatty acids and glycerol are also discussed, alongside hormonal regulation. In addition, the synthesis of fatty acids is described as an important anabolic pathway occurring under energy-rich conditions. The role of lipoproteins in lipid transport and their clinical significance in metabolic disorders are highlighted. The review concludes with an in-depth detailing of the structure and function of the cell membrane, focusing on the fluid mosaic model, membrane components, and transport mechanisms. This review integrates biochemical and structural perspectives to provide a detailed understanding of lipid metabolism and membrane dynamics, with relevance to both normal physiology and disease states.