PostgreSQL is a popular and reliable open-source relational database management system. psql is an interface that allows users to interact with Postgres databases through the terminal. This article covers essential psql commands and flags, including connecting to a database, listing all available databases, switching between databases, describing tables, listing schemas, viewing user roles, saving query results to files, running commands from files, and quitting psql. Additionally, it introduces Hasura as an option for generating APIs for data access on Postgres.