web application to download on server

I'm a experienced software developer but beginner at web development. I'm making one site with the ability to download torrents on web hosting server that I'm gonna buy(frm godaddy or hostgator). All I want to do is open up my site, give it a torrent link or upload one and press download and close it. And after a while open it again to check the progress and if it's completed then just download it directly. I'm NOT asking for the code. All I'm asking is that how to code an application that keeps running in background(on server side) to download the torrents. I can code a site but don't know how to do this. Tell me how to do it, which language or framework to use and how to do it? What is the procedure to code this kind of application?

thanks