You care able to use external form tools with Website Builder.
Website Builder has two types of forms
Click on the Widgets tab (1) and then drag and drop either of the two form widgets (2) (3) onto the page.
If you need a more complex form, try using the embed widget
If you need a more complex form, you can use the embed widget (1) to display forms made with tools like JotForm or Wufoo or any other form builder that has Responsive form templates.
Example: Creating a booking form with Jotform
You will need to create an account at http://www.jotform.com/
The free account supports up to 100 form submissions per month.
Find a responsive form template
Click on the Form Templates button (1) and then search for "responsive" (2). A list of responsive form templates will be displayed (3)
Edit the form
Edit the form using the tools provided.
Get the embed code
Click the Setup & Embed tab (1) and then click the Source Code button (2). Copy the source code (3).
In Website Builder, drag an embed widget onto the page
Click the widgets tab (1) and drag an Embed widget (2) into the page (3).
Click the Embed widget
Click on the widget to open the code editor
Paste the form code
Paste the form code and click the save button (1)
Test the form
Click the Preview button (1) to test the form. The form will not work in page edit mode - you must use Preview.
Publish your site to make the form visible online.