Codeigniter libraries : Codeigniter libraries provides you rich functionality with ready made libraries. You can also create your own library.
Using Codeigniter libraries
$this->load->library('library_name');
For Example If We Need Form validation library
$this->load->library('form_validation');
Load Multiple Codeigniter libraries
$this->load->library(array('form_validation','email'));
You Can Also Auto-load Libraries
Go to application/config/autoload.php
Now go to the below lines and add the library name you want to automatically load.
$autoload['libraries'] = array('email','form_validation');