Using HubSpot forms to your advantage
HubSpot forms help you gather new contacts for your company and obtain additional information from your existing contacts.
When editing a HubSpot landing page, you can link a form to it by using the Form drop-down menu to select the form you created. Please note that your landing page must contain a Form module in order to add the form.
HubSpot understands that some of our customers maintain a website not hosted on HubSpot, but still want the ability to capture lead information and store it in HubSpot. We provide two options: Forms API and the form embed code. Using the embed code gives you access to all of the benefits of HubSpot forms like contacts database integration, smart fields, and progressive profiling (Professional and Enterprise accounts), on your external site with the HubSpot tracking code installed. In order to take advantage of all of HubSpot's form functionality, the tracking code should be on each web page you have live before adding form embed code.
Resource: Using HubSpot forms on your external website & How to create a lead flow