Plug form into Process Engine

Hi all,
I want to let my process engine know that there is one form engine too linked to one of task’s of the process.
I was reading this doc :

But here it isnt mentioned how programatically we can link a form engine to process engine. Could anyone help.
Secondly ,so far i could comprehend from form and process is that we can associate any form with process task. Is my understanding correct.

thanks in advance