You can't, at least not here at x10Hosting. That application (it's far more than a "script") is a Python/Django app, and the only server-side language supported on the Free Hosting servers here is PHP. You need at least Python hosting (and it would really help if the Django platform was already installed).
Oh, and despite the protestation in the site footer to the contrary, it very much is a Stack Exchange clone. The idea's been done. There is a reference implementation. There are available Markdown parser/sanitizer/converters for PHP and JavaScript with very liberal licenses. jQuery can handle most of the rest of the UI interactivity (votes, comments, etc.) easily. In other words, there's nothing stopping an enterprising young person from implementing this in PHP and MySQL if they've a mind to.