To add a form to you Google Sites page, go to Publish → Google Sites and spot the link generated for your form.
Access your Google Sites page and press Edit page (top right corner). Then select Insert in the horizontal menu (top left corner) and choose More gadgets. Press Add gadgets by URL in the left panel. Paste your form URL (generated in the Publish → Google Sites section) in the provided box and press Add.
The next step concerns customizing display settings. Choose the width of the gadget that will contain your form (percentual or in pixels) and set its height. It is important to set a large height size (at least 800 pixels).Set other available options and press OK. Finally, press Save in your main view.
The web form will not be visible in the editor, but in regular view mode. Press Save on the top right side and you’ll see the form on the web page after refresh. You can now share your web page with others and collect the leads or contacts you need.