There are several configuration files in CodeIgniter that you can use to customize the behavior of your application.

The main configuration file is application/config/config.php, which contains settings such as your base URL, index page, and encryption key. Here are some of the important configuration options in this file:

• $config['base_url']: The base URL of your application. This should include the protocol (e.g., http or https) and the domain name, but should not include the trailing slash.

• $config['index_page']: The name of the index page of your application. By default, this is set to index.php, but you can change it to something else or set it to an empty string if you are using URL rewriting.

• $config['encryption_key']: A random string that is used for encrypting and decrypting data. You should set this to a long, random string for security.

The application/config/database.php file contains your database connection settings. You need to set the hostname, username, password, and database name for your MySQL database.

Other configuration files include:

• application/config/routes.php: This file allows you to customize the default routing behavior of your application.

• application/config/autoload.php: This file lets you specify which libraries, helpers, and models should be autoloaded by default.

• application/config/constants.php: This file allows you to define custom constants for your application.

You can access the configuration options in your controllers using the $this->config->item() method. For example, to get the base URL of your application, you can use $this->config->item(‘base_url’).