Whereas Helix provides a limited set of format options, HTML is quite varied. Let's suppose you want to output a graphic, based on a client's request. When the HTML is formatted by the client's browser, the client will follow the reference and retrieve the graphic. In other words, Helix does not download the graphic, but merely tells the client where to go an get it. The web server is a critical link between the client browser and Osmosis.
Clients communicate directly with the web server.
Osmosis, in turn, tells the web server to wait for a reply - and when received, send the reply back to the client. All of this communication happens behind the scenes, assuming some configuration has been done beforehand. Within this file, there are specific statements passed to the web server when the form is submitted. These statements tell the web server what to do with the form data. Specifically, different file types require different 'actions'.