The reference folder is the /catalog/ folder of your osCommerce installation.
1) Unpack the Zip File and copy the files into the corresponding folders and sub-folders.
2) Open the file includes/languages/english.php.
Scroll down to the very end and paste before the "?>"-statement the following text:
define('SELLECTOR_LINK', 'Click here, to start the Sellector.');
Feel free to change the text between the inverted commas to your needs.
3) Open the file includes/column_left.php an paste in line 26:
require(DIR_WS_BOXES . 'sellector.php');
4) Open the file sellector.php and change in line 49 the corresponding parameters!
Now you can start including Sellectors into your osCommerce shop.