To add a form to your Google Sites page, go to Publish – Embed.
Place the form in the section you need it on your webpage. Drag the corners to adjust the form’s element height and width.
Finally, press Publish to save the changes to your website. You can now share your web page with others and collect the leads or contacts you need.
If you are using the old version from Google Sites, use the iframe code of your form (Embed Code – Iframe)