The emergence of the World Wide Web has revolutionized online communication, aiming to achieve global information sharing and communication. However, the current Web 2.0 architecture, which relies on centralized platforms, presents limitations such as restricted user rights, data privacy concerns, and dependence on centralized institutions. Web3, as a concept describing the next evolutionary stage of the internet, offers a solution to these issues by reshaping the internet infrastructure. Web3 provides a foundation for autonomous digital experiences and drives the advancement of the digital economy. This paper offers a thorough exploration of Web3, covering its key technologies, applications, challenges, and opportunities. We begin by introducing the core technologies behind Web3, followed by an exploration of its prominent applications. Finally, we analyze the challenges faced by Web3 and discuss potential research opportunities to address these challenges in the future. In summary, this study comprehensively elaborates on Web3 and lays a solid foundation for subsequent research work, encouraging researchers to explore new frontiers.