The primary function of relational databases is to store, manage, and retrieve data in a structured format, using tables to define relationships among the data. These databases operate using Structured Query Language (SQL) to perform operations such as inserting, updating, and querying data, which can be complex and interconnected. By organizing data in tables with predefined schemas, relational databases ensure data integrity and provide powerful capabilities for data analysis and reporting. Popular systems include Oracle, Microsoft SQL Server, and PostgreSQL.