The integration of satellite and terrestrial networks is poised to play a critical role in 6G, enabling seamless global connectivity and extending coverage to underserved and remote areas. This paper explores the fusion of satellite communication with traditional ground-based infrastructure to create a hybrid network that offers high throughput, low latency, and ubiquitous connectivity. We examine the challenges of interoperability, spectrum management, and the dynamic coordination required between satellite constellations (LEO, MEO, and GEO) and terrestrial networks. The paper also discusses how advanced techniques such as network slicing, AI-driven resource allocation, and hybrid beamforming can optimize performance across these diverse platforms. Furthermore, we highlight key applications, including global internet access, IoT, and disaster recovery, that will benefit from satellite-terrestrial integration. Ultimately, this paper provides insights into how satellite-terrestrial hybrid networks can become a cornerstone for 6G, ensuring reliable, high-performance communication worldwide.