This video explains how to use the CREATE INDEX statement of the Structured Query Language (SQL). It is the third in a series about a subset of SQL known as the Data Definition Language (DDL), which can be used to create and modify the table structures within a relational database. It includes examples of how to use CREATE INDEX and CREATE UNIQUE INDEX to add single column index, and multiple column indexes, also known as composite indexes, to a table. It also covers how to use drop index to remove an index from a table. Some variations between MySQL, SQL Server and Microsoft Access are mentioned. The SQL Server specific CREATE CLUSTERED INDEX and CREATE NONCLUSTERED INDEX statements are specifically mentioned.