The nitrogen-vacancy (NV) center in diamond has quickly developed into one of the most versatile and dynamic solid-state quantum platforms, encompassing condensed matter physics, emerging quantum technologies, nanoscience, and life sciences. This prominence stems from its unique combination of properties: Millisecond-scale spin coherence at room temperature, atomic-scale spatial resolution, non-invasive and non-destructive operation, remarkable chemical stability, excellent biocompatibility, and the tunable coupling strength to multiple physical fields. Its electron spin can be efficiently initialized by laser illumination and precisely manipulated via microwave resonance, enabling high-sensitivity detection of magnetic and electric fields, temperature, stress, and spin signals, with some experiments already achieving single-nuclear-spin or single-electron-charge resolution. In this review, we start with a brief overview of the fundamental properties of the NV center, clarifying the influences of spin-orbit coupling, hyperfine interactions, and other key effects on its energy level structure. We then systematically outline the fabrication methods for creating NV centers with high spatial control and spectral quality. Finally, we provide a detailed exposition of how NV centers are used for nanoscale sensing and measurement across various physical domains, highlighting both established protocols and recent experimental advances. Through this structured presentation, the review aims to provide a coherent and up-to-date resource for researchers exploring the interdisciplinary potential of diamond NV centers.