How to change where an HTML form redirects after submit?

[James Z]

How do you choose what page a basic HTML form sends the person who fills it out to after it is submitted? For example, if I wanted the form to go to www.poop.com/thanks.html after the person hits the submit button, how would I do this? As of now, when the submit button on my site is hit, it redirects them back to the index.html page..thanks for your help