Handlebar Templates are defined in the uiProperties file in the cloudcraze managed package. This file contains various properties that control the behavior and appearance of the user interface components. The handlebarTemplates property defines a map of template names and template contents that are used by the handlebars.js templating engine to generate HTML from JSON data. Salesforce Reference: B2B Commerce and D2C Commerce Developer Guide, UI Properties, Handlebars Templates

Two Salesforce B2B Commerce Visualforce pages that must be enabled at a Salesforce Community level to make the out of the box SEO functionality available are:
CCSizeIndex: This page generates a sitemap.xml file, which is a file that lists all the pages and resources on a site that can be crawled by web crawlers. The page uses the configuration settings CO.SiteMapIncludeProducts and CO.SiteMapIncludeCategories to specify which products and categories should be included in the sitemap.
CCCatSiteMap: This page generates a category sitemap file, which is a file that lists all the categories on a site that can be crawled by web crawlers. The page uses the configuration setting CO.SiteMapCategoryDepth to specify how many levels of subcategories should be included in the category sitemap. Salesforce Reference: B2B Commerce and D2C Commerce Developer Guide, Sitemap Files

To have a Contact Us page in the storefront that is a web-to-lead form and has the same look and feel as all the pages in the application, the requirement can be fulfilled by creating a Subscriber Page (CC Page). This is a custom Visualforce page that can be added to the storefront and use the standard header and footer components. The page can also include a web-to-lead form that submits data to Salesforce as leads. Salesforce Reference: B2B Commerce and D2C Commerce Developer Guide, Subscriber Pages

The correct answer for what is true about mapping custom fields from Cart to Order Summary is that the automatic Cart to Order mapping of custom fields can be disabled. A custom field is a field that is added by a developer or an administrator to an object to store additional information or data. A Cart is an object that represents a collection of products and charges that a customer intends to purchase in the storefront. An Order Summary is an object that represents a confirmed purchase of products and charges by a customer in the storefront. A Cart can be converted to an Order Summary when the customer completes the checkout process and confirms their order. By default, Salesforce B2B Commerce automatically maps custom fields from Cart to Order Summary when converting a Cart to an Order Summary. This means that any custom fields that exist on both Cart and Order Summary objects with identical API names and data types will have their values copied from Cart to Order Summary during the conversion. The automatic Cart to Order mapping of custom fields can be disabled by setting the B2BCommerce.CartToOrderMappingEnabled custom setting to false. This will prevent any custom fields from being copied from Cart to Order Summary during the conversion. A custom field must exist in the Cart and Order Summary objects only to be mapped successfully is not true, as it is not the only requirement for mapping custom fields from Cart to Order Summary. The custom fields must also have identical API names and data types, and the automatic Cart to Order mapping of custom fields must be enabled. All data types are supported for custom fields to be mapped from Cart to Order is not true, as some data types are not supported for mapping custom fields from Cart to Order Summary. The supported data types are Boolean, Date, DateTime, Double, Integer, Long, Percent, String, and TextArea. There is a limit of 25 custom fields on a Cart that can be mapped to Order is not true, as there is no such limit for mapping custom fields from Cart to Order Summary. Any number of custom fields that meet the mapping requirements can be mapped from Cart to Order Summary. Salesforce Reference: [B2B Commerce Developer Guide: Custom Field Mapping], [B2B Commerce Developer Guide: Cart Object], [B2B Commerce Developer Guide: Order Summary Object]