Intelligent Reflecting Surface (IRS) is a promising technology for enhancing wireless communication by dynamically altering wireless channels through smartly tuned passive reflecting elements. IRS can be deployed in wireless networks to improve spectral and energy efficiency, enabling sustainable capacity growth. However, challenges such as reflection optimization, channel estimation, and deployment need to be addressed. This paper provides a tutorial overview of IRS-aided wireless communication, discussing its reflection and channel models, hardware architecture, practical constraints, and applications. It highlights important research directions for future work. IRS is a planar surface with many passive reflecting elements that can independently control the amplitude and phase of incident signals. By deploying IRSs in wireless networks and coordinating their reflections, signal propagation between transmitters and receivers can be flexibly reconfigured. This allows for improved communication performance by mitigating channel fading and interference. IRS offers practical advantages such as low hardware and energy costs, full-duplex operation, and compatibility with existing wireless systems. IRS can be used in various applications, including coverage extension in mmWave and THz communications, improving signal power at cell-edge users, and enhancing SWIPT efficiency. It can be deployed on various surfaces, such as ceilings, walls, and building facades, to support a wide range of applications. IRS is a disruptive technology that can make environments intelligent, benefiting vertical industries like transportation, manufacturing, and smart cities. The paper discusses the fundamentals of IRS-aided wireless communication, including signal and channel models, hardware architecture, and practical constraints. It addresses passive reflection optimization, channel estimation, and deployment under various system setups. The paper also discusses the impact of IRS on future wireless networks, including the shift from traditional M-MIMO systems to IRS-aided systems and from heterogeneous networks to hybrid networks. The paper concludes that IRS is a promising technology for future wireless networks, offering new opportunities and challenges. It emphasizes the need for further research in IRS-aided wireless communication, including reflection optimization, channel estimation, and deployment strategies. The paper provides a comprehensive overview of IRS-aided wireless communication, highlighting its potential to revolutionize future wireless networks.Intelligent Reflecting Surface (IRS) is a promising technology for enhancing wireless communication by dynamically altering wireless channels through smartly tuned passive reflecting elements. IRS can be deployed in wireless networks to improve spectral and energy efficiency, enabling sustainable capacity growth. However, challenges such as reflection optimization, channel estimation, and deployment need to be addressed. This paper provides a tutorial overview of IRS-aided wireless communication, discussing its reflection and channel models, hardware architecture, practical constraints, and applications. It highlights important research directions for future work. IRS is a planar surface with many passive reflecting elements that can independently control the amplitude and phase of incident signals. By deploying IRSs in wireless networks and coordinating their reflections, signal propagation between transmitters and receivers can be flexibly reconfigured. This allows for improved communication performance by mitigating channel fading and interference. IRS offers practical advantages such as low hardware and energy costs, full-duplex operation, and compatibility with existing wireless systems. IRS can be used in various applications, including coverage extension in mmWave and THz communications, improving signal power at cell-edge users, and enhancing SWIPT efficiency. It can be deployed on various surfaces, such as ceilings, walls, and building facades, to support a wide range of applications. IRS is a disruptive technology that can make environments intelligent, benefiting vertical industries like transportation, manufacturing, and smart cities. The paper discusses the fundamentals of IRS-aided wireless communication, including signal and channel models, hardware architecture, and practical constraints. It addresses passive reflection optimization, channel estimation, and deployment under various system setups. The paper also discusses the impact of IRS on future wireless networks, including the shift from traditional M-MIMO systems to IRS-aided systems and from heterogeneous networks to hybrid networks. The paper concludes that IRS is a promising technology for future wireless networks, offering new opportunities and challenges. It emphasizes the need for further research in IRS-aided wireless communication, including reflection optimization, channel estimation, and deployment strategies. The paper provides a comprehensive overview of IRS-aided wireless communication, highlighting its potential to revolutionize future wireless networks.