Just upload these files into your CodeIgniter application folder and set the config variables. You can then load the library like this
  $this->load->library('googleplus');

Example usage:
  $this->googleplus->people->get('me'); // when authorized
  $this->googleplus->people->get('115414977082318263605'); // that's me :-)
  
Read the full API docs on the Google+ website http://developers.google.com/+/api

Uses the Google APIs Client Library for PHP
http://code.google.com/p/google-api-php-client/