Follow given steps to install CodeIgniter :
1. Download CodeIgniter from official website : here
2. Unzip the package.
3. Open the codeigniter project on browser
4. Open your application/config/config.php file with a text editor and set your base URL. If you intend to use sessions set your encryption key.
5. If you want to use a database, open the application/config/database.php file with a text editor and set your database settings.