ACL stands for Access Control List. In CakePHP, ACL is a component of the authorization and authentication system that allows you to control which users have access to which controllers, actions, and resources.

To use ACL in a CakePHP application, you will need to follow these steps:

1. Enable the CakePHP ACL plugin: The ACL plugin provides a set of components and behaviors that can be used to implement ACL in your application. To enable the plugin, add the following line to your application’s config/bootstrap.php file:

Plugin::load('Acl', ['bootstrap' => true]);

2. Set up the database tables: The ACL plugin uses a set of database tables to store the authorization rules. You will need to create these tables and populate them with the appropriate data. You can use the initdb shell command to create the tables:

bin/cake acl_extras initdb

3. Set up the ACL component: You will need to set up the AclComponent in your application’s controller to handle the ACL logic. You can do this by adding the following line to your controller’s initialize method:

$this->loadComponent('Acl.Acl');

4. Use the Acl->check method: You can use the Acl->check method in your controller’s actions to check if a user has the appropriate permissions to access a particular resource. For example:

if ($this->Acl->check($user, 'Posts', 'view')) {
  // Allow the user to view the post
} else {
  // Deny access
}

By following these steps, you should be able to use ACL in your CakePHP application to control access to controllers, actions, and resources.

Note: These are just the basic steps for using ACL in CakePHP. There are many additional customization options available, such as creating custom authorization rules and using the Acl->allow and Acl->deny methods to grant and revoke access. You can refer to the CakePHP documentation for more information.