The SELECT statement is used to query a database and retrieve a subset of data that matches the specified criteria. For example, SELECT * FROM Customers WHERE City = 'London' will return all the records from the Customers table where the City column is equal to 'London'. The SELECT statement can also be used to join multiple tables, perform calculations, sort and group data, and apply filters and functions. The SELECT statement is one of the most commonly used SQL commands and is essential for manipulating and analyzing data in a database.