See http://www.nutshell.com/api/http-post-api.html for more details

nutshell-post-api-example.html

<form action="https://app01.nutshell.com/YOUR_URL_HERE" method="post">
	Company name: <input name="account[name]" type="text"> <br>
	Company email: <input name="account[email]" type="text"> <br>
	
	Your name: <input name="contact[name]" type="text"> <br>
	
	<textarea name="note" placeholder="Comments"></textarea>
	
	<input name="ok" value="Submit" type="submit">
	
	<!-- only hidden fields below -->
	
	<!-- This product must already exist in Nutshell -->
	<input name="product[name]" value="Clamcase" type="hidden">

	<!-- This source must already exist in Nutshell -->
	<input name="source[name]" value="Web form" type="hidden">
	
	<input name="successUrl" value="http://mysite.com/thanks.html" type="hidden">
	<input name="errorUrl" value="http://mysite.com/form.html" type="hidden">
</form>