Carbohydrates are essential biomolecules that play a variety of structural and functional roles in living organisms. As one of the three major macronutrients, along with proteins and fats, carbohydrates are a vital energy source and metabolic fuel. However, carbohydrates contribute much more than just calories. This review provides an in-depth examination of carbohydrate chemistry, structure, function, and metabolism. Focus is given to how the specific molecular structures of different carbohydrate classes including monosaccharides, disaccharides, oligosaccharides, and polysaccharides determine their physiological activities. Key topics covered include carbohydrate digestion and absorption, glycoprotein and glycolipid synthesis, energy storage, and cell signaling roles. Special attention is paid to glucose metabolism and homeostasis due to the critical importance of blood sugar regulation. Potential links between carbohydrate structures and the development of metabolic disorders are also discussed. Tables and figures are provided to illustrate key concepts and summarize important information. Current areas of research and future directions are highlighted to demonstrate how continued elucidation of carbohydrate structural chemistry may lead to improved understanding of carbohydrate biology and better therapeutic interventions for carbohydrate-related diseases. This broad review provides a structural perspective to improve comprehension of the diverse functional roles of carbohydrates in biological systems.