How to use psr-4 in composer with different subfolders

How do you configure my directories in composewr.json,

My directories are like this and are not right

Vizuare
  -vendor
    -composer

    -php-class
       -src
         -DB
         -Model
         -Page.php


    -phpmailer
    -rain
    -slim
    -autoload.php

-views
-views-cache
composer.json
composer.lock
index.php

Why is not my folder structure working?