To use you just need static submit function which takes to arguments.
public static function submit($data, $w2l_file)$data is the data you want to submit to salesforce.com through their
web-to-lead form
$w2l_file is the path to the web-to-lead HTML file downloaded from
salesforce.com when generating Web-To-Lead.
The library will parse the HTML file and generate the structure of the data that SF accepts.
After it normalizes the data based on the structure, cleans up empty
fields and decodes for custom fields with tokens in name= attribute.
And after all that it will POST the form to the URL in the web-to-lead
HTML file form action= attribute.