1 Download Codeigniter from this below link
2 After Download zip file, extract it and copy all file and folder in your project.
3 Then Run your project, you can see first screen.
welcome to codeigniter
then in bottom you can see you userguide. This userguide provide us help.
In codeigniter there are three type of folder available
1- Application Basically we work on only application folder.
2- System contains codeigniter libraries,helper and other files etc,we are just load these(libraries and helper) and use for webdevelopment.
3- User_guide This is offline user guide, this is provide help for developer, this is explain everything like libraries, helper etc Developer can easily learn and use for development.
Cache − This folder cached all pages so that speed of your website increase. In this folder we are not doing any work.
Config − We can configure the application like config.php for base url , database.php for database name , autoload.php for load Helper, Libraries, Models etc
Controllers − This is starting place of project, Basically we run controller, everything start from here and will comunicate model and view.
Core − We create base class of your application.
Helpers − We can put helper class of your application.
Hooks − We can do inner workings of the framework without hacking the core files.
Language − This folder contains language related files.
Libraries − This folder contains files of the libraries developed for your application.
Logs − This folder contains log of the system.
Models − In this folder we create login like insert record into database etc. Third_party − We can place any plugins.
Views − We create all Website HTML page here.