Within the form code, the ‘action’ tells the form to submit this information through SalesForce.
action="https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8"
When a form is submitted, Google Analytics tracks the user’s click and registers it as a unique form submission.
<input type="submit" id="submit-button" value="Submit" onClick="ga('send', 'event', { eventCategory: 'SalesForce', eventAction: 'SalesForce Solar Quote', eventLabel: 'Solar Quote'});" >