What step must be taken before using the PDO class in PHP?

Before using the PDO class in PHP, the first necessary step is to instantiate a new PDO object. The PDO (PHP Data Objects) class provides a data-access abstraction layer, which enables you to interact with different types of databases in a unified manner. This instantiation involves creating a new instance of the PDO class and requires certain parameters, such as the Data Source Name (DSN), username, and password for accessing the database.

By creating a new PDO object, you enable your script to connect to the database, after which you can perform further operations such as executing queries and handling results. This initial object creation is fundamental, as it sets up the connection and prepares the environment for database interactions.

Other actions, like setting error modes or checking for database existence, might be involved in the process of robust database handling but occur after the PDO object has been instantiated. Thus, the instantiation of the PDO object is the critical first step before any other related operations can take place.