Structure

Source : https://codeigniter.com/user_guide/concepts/structure.html

/app
    /Config         Stores the configuration files
    /Controllers    Controllers determine the program flow
    /Database       Stores the database migrations and seeds files
    /Filters        Stores filter classes that can run before and after controller
    /Helpers        Helpers store collections of standalone functions
    /Language       Multiple language support reads the language strings from here
    /Libraries      Useful classes that don't fit in another category
    /Models         Models work with the database to represent the business entities.
    /ThirdParty     ThirdParty libraries that can be used in application
    /Views          Views make up the HTML that is displayed to the client.
    
/public             Application assets that you add, like CSS, javascript, or images.
    /upload         Upload folder location

/system             This directory stores the files that make up the framework, itself.