Authentication is the process of verifying a user's identity and plays a crucial role in accessing protected apps, services, and networks. There are five major types of authentication: username and password, multi-factor authentication, token-based authentication, certificate-based authentication, and biometric authentication. Each type varies based on factors like security, ease of implementation, and the method used to verify identities. The choice of authentication method depends on the level of security required, user convenience, and the nature of the app or service being accessed.