How do I auto-complete third-party components?

Question

Yii

I really want to get an autocomplete of third-party components. I found this article, but I can’t understand where to throw all these files to make it work? I understand there will be two files: Yii.php and User.php.
1. Suppose I can throw a webuser into the components folder, since he is in this namespace,
2. where to throw Yii.php? in the web folder? Or even at the root of the project?
3. In addition, after these machinations, I always underline the Yii class and write "Multiple definitions exist for class Yii".
4. Is it necessary in the web/index.php file instead of (new yii\web\Application($config))->run(); write (new WebApplication($config))->run(); ? And instead of require __DIR__ . '/../vendor/yiisoft/yii2/Yii.php'; request my Yii.php.
5. And similarly for the root yii file that controls the console application.