This review introduces Rydberg excitons as highly excited electron-hole pairs in semiconductors, highlighting their core characteristics: hydrogen-like energy levels, macroscopic quantum properties, strong interactions, and nonlinear optical response. It elaborates on cuprous oxide (Cu₂O) as an ideal platform for observing high-order Rydberg states due to its low defect density and dipole-forbidden transitions. The analysis covers key properties of Rydberg excitons revealed through spectroscopic techniques and external field manipulation: micron-scale radii, high polarizability, long lifetimes, and large dipole moments. It further discusses the significantly enhanced long-range interactions between excitons at high principal quantum numbers, which lead to phenomena like excitonic blockade and nonlinear refraction. The discussion extends to the modulation of excitonic properties by external fields, including field-induced energy level splitting, alteration of transition selection rules, and selective excitation of specific states, while also noting the impact of environmental perturbations on spectral features. It is pointed out that Rydberg excitons have great potential for applications in cutting-edge fields such as weak-field sensing, on-chip single-photon devices, quantum simulation, and microwave-to-optical signal conversion due to their distinctive physical attributes and extreme sensitivity to external fields and the environment. The review proposes that in-depth research and exploitation of these properties represent a crucial direction for advancing high-performance quantum information technologies and precision sensing in the future.