View source for Basic form guide

=== Step 4 User Submitting the Form ===
The user enters data into your HTML form and clicks on the submit button. The browser generates an HTTP POST request to the URL specified in the ''<form>'' element and passes to the server in POST parameters the values entered by the user; each parameter keyed by the "name" attribute of the HTML input element.

Joomla routes this POST through to your component. As this is a new HTTP request the previous Form instance no longer exists, so you have to again call ''Form::getInstance()'', passing the filename of your form XML, and Joomla (as before) creates a Form instance and reads this file into memory.