Codeigniter installation :
1. Download the latest codeigniter file from https://codeigniter.com/
2. Unzip the package and move into htdocs(xampp) or Www(wamp)
3. Type the installtion path in URL http://localhost/demo_codeigniter
4. Change base_url path in config/config.php as http://localhost/demo_codeigniter
5. change the database name, database username, database password and host.
6. change the autoload file in config/autoload.php file .
Include url in $autoload['helper'] = array('url');
7. Then create controller at application/controllers/demo_file.php
8. Create view file at application/views/demo_view.php and load the view file into the controller $this->load->view('demo_view').
9. Run the http://localhost/demo_codeigniter/demo_file.