This tutorial provides a comprehensive overview of physical layer security (PLS) techniques for next generation multiple access (NGMA) networks, particularly focusing on non-orthogonal multiple access (NOMA). As wireless networks evolve to meet the demands of ultrahigh spectral efficiency, ultra-low latency, and massive connectivity, NGMA is being developed to support these requirements more efficiently than traditional orthogonal multiple access (OMA). However, NOMA's open air interface and broadcast characteristics introduce significant security challenges, such as eavesdropping, signal leakage, and interference. To address these issues, PLS techniques are being explored as an efficient and cost-effective alternative to cryptographic methods, which are often computationally intensive and may introduce latency. PLS techniques leverage the physical characteristics of wireless channels, such as fading, interference, and noise, to achieve different levels of security and privacy, including information-theoretic security, quantum-safe security, and low probability of detection (covertness). These techniques can be enhanced by integrating emerging 6G technologies such as intelligent surfaces, cooperative relays, large antenna arrays, quantum computing, and ambient backscatter communication. The tutorial reviews the fundamentals of NOMA and PLS, discusses the challenges and opportunities in securing NOMA communications, and highlights the latest research in information-theoretic security, quantum-safe security, and covert communication. It also outlines important research directions for future work, including the potential of integrated sensing and communication (ISAC), satellite communication, new spectrum resources, net zero communication, and generative AI in securing NOMA systems. The tutorial concludes with a summary of the key findings and future research directions in the field of PLS for NGMA networks.This tutorial provides a comprehensive overview of physical layer security (PLS) techniques for next generation multiple access (NGMA) networks, particularly focusing on non-orthogonal multiple access (NOMA). As wireless networks evolve to meet the demands of ultrahigh spectral efficiency, ultra-low latency, and massive connectivity, NGMA is being developed to support these requirements more efficiently than traditional orthogonal multiple access (OMA). However, NOMA's open air interface and broadcast characteristics introduce significant security challenges, such as eavesdropping, signal leakage, and interference. To address these issues, PLS techniques are being explored as an efficient and cost-effective alternative to cryptographic methods, which are often computationally intensive and may introduce latency. PLS techniques leverage the physical characteristics of wireless channels, such as fading, interference, and noise, to achieve different levels of security and privacy, including information-theoretic security, quantum-safe security, and low probability of detection (covertness). These techniques can be enhanced by integrating emerging 6G technologies such as intelligent surfaces, cooperative relays, large antenna arrays, quantum computing, and ambient backscatter communication. The tutorial reviews the fundamentals of NOMA and PLS, discusses the challenges and opportunities in securing NOMA communications, and highlights the latest research in information-theoretic security, quantum-safe security, and covert communication. It also outlines important research directions for future work, including the potential of integrated sensing and communication (ISAC), satellite communication, new spectrum resources, net zero communication, and generative AI in securing NOMA systems. The tutorial concludes with a summary of the key findings and future research directions in the field of PLS for NGMA networks.