In short, webhooks allow you to send Marketo data to another system through a flow step.
Without getting too deep into the details, if you have an external site that can accept data via a URL with paramaters, you can use webhooks to send the data to that site without posting the URL visible to the user.
For example, you might be able to create a database record for John Smith and SmitthCo.com using a URL like this:
http://www.SmithCo.com/addNewRecord.do?xxxxx=email@address.com&yyyyy=John&zzzzz=Smith
To create a Webhook, you simply separate the two sections, then use Marketo tokens to send the parameter data. When you look at the Create Wehbook form in the Admin section, there's two boxes to fill--URL and Template.
The URL is the piece up to and including the question mark:
http://www.SmithCo.com/addNewRecord.do?
The Template is the coded paramers using token
xxxxx={{lead.Email Address}}&yyyyy={{lead.FIrst Name}}&zzzzz={{lead.Last Name}}
where xxxxx, yyyyy, and zzzzz are the field names in the external system, and Email Address, First Name, etc are the Marketo field names.
A use case might be a situation where you want someone to sign up using a marketo form, display a marketo thank you page, but send the collected data to an external system.
Your Smart Campign would be a simple:
Trigger: Fills Out Form = Form Name
Flow: Call Webhook = Webhook Name
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