Unable to add Form to a Page using Site.com

Hii Karen,

When you are using a template while creating page for site.com then you cannot use an Data and Form components as these are not available for use when editing community site in site.com. The Form, Data and some other page elements on the site.com studio will also be not visible if existing template pages are used .

This is an known issue in Salesforce introduced in winter'15 release. Please see here for more info.

In case if you want to add a form then in that case you will to delete all the pages and then create a new page and add the forms according to your requirement.

Thanks.