In your HubSpot account, navigate to Reports > Analytics Tools. Then, select Events.
In the events dashboard, click Create event in the upper right.
In the pane that slides in on the right, enter an Event name, and select Tags (optional) to easily find and keep track of your event. Select Submitted form as the Event type, then click Next at the bottom right.
In the Form dropdown, select a HubSpot form. If you're using an external form via the Forms API, select the corresponding HubSpot form you're posting to. To track non-HubSpot forms that don't use the Forms API, you'll need to use custom events.
If you have the form placed on multiple pages and only want to track one instance of it, enter the Page URL.
Click Save at the bottom right to finish creating your submitted form event.