API Features provides features such as filtering, sorting, limiting fields, and pagination for API queries. It takes in a query and queryString as constructor parameters and modifies the query object based on the provided query parameters.
Authentication is performed by sending a JWT (JSON Web Token) to the user in the 'headers' when they sign up or log in to the website. This allows for secure access to certain features or information on the website and ensures that the user's identity is verified.