The crisis of classical physics, marked by experiments such as Michelson-Morley's and observations on blackbody radiation, led to the development of quantum theory. The concept of energy quantization introduced by Planck, followed by Einstein’s ideas on the quantum nature of light, revolutionized the understanding of microscopic physical phenomena. This thesis explores the connection between entanglement and non-locality, with a particular focus on continuous-variable systems, an area crucial for applications in quantum computing and metrology. The work begins with a discussion on the quantum theory of light, analyzing electromagnetic field quantization and introducing fundamental states such as Fock, coherent, and squeezed states.