This paper examines the influence of social media on consumer purchase decisions and brand perception. It defines, classifies, and highlights the primary functions of social media, and analyzes its role at each stage of the consumer decision-making process—problem recognition, information search, alternative evaluation, purchase choice, and post-purchase behaviours. The study demonstrates that social media significantly shapes consumer behavior, brand attitudes, and brand perception through content sharing, social validation, and interactive engagement. Emerging challenges and future research directions, such as artificial intelligence, virtual reality, cross-platform integration, and corporate social responsibility, are also discussed. Overall, social media not only offers new avenues for influencing purchase behavior but also plays a critical role in shaping how consumers perceive and relate to brands. To remain competitive, brands must innovate in information dissemination, engagement strategies, and perception management across social platforms.