Trish, could you please describe what you are hoping to accomplish with webhooks in Machform? Perhaps using a webhook isn't the best way to accomplish your task.
Basically, webhook is the name of a concept; a way of connecting or "hooking" (the hook part) two websites (the "web" part) together. Machform has a specific version of this idea, which allows Machform to send information to other websites so you can use the data collected by your forms in Machform to update information (such as records or configuration settings) on another website such as Mailchimp.