marketinginfo on "[Plugin: Contact Form 7] custom submit action"

could I use a custom submit action ?
I read about [submit] clause but I didn't understand.

My need is to call a custom php file from which I can manage the fields that visitors inserted in CF7.

I also need to know how to refer to my fields (GET/POST/whatelse ?)

http://wordpress.org/extend/plugins/contact-form-7/