http://devnet.kentico.com/docs/7_0/devguide/index.html?document_properties_overview.htm
You can edit document properties in CMS Desk -> Content after selecting a document in the content tree and opening the Properties tab in Edit mode.
Template
http://devnet.kentico.com/docs/7_0/devguide/index.html?document_properties_template.htm
In the Template dialog, you can specify the page template that will be used for the selected document and configure its content inheritance.
Template
The textbox in this section displays the name of the page template currently assigned to the document. The options above determine what type of template will be used:
•Inherit from parent
•All culture versions use the same page template
•Each culture version uses its own page template
If the first option is selected, the page template set for the parent document will automatically be loaded.
With the other two options, you can assign a specific template to the document via the Select button. If the document is available in multiple languages, you can choose whether all versions should share the same template or if it should be possible to specify a different one for each language. By selecting the third option, you can configure the template settings on this tab separately for each document version by switching between cultures using the language toolbar in the main menu of the CMS Desk -> Content tab.
Changes need to be confirmed by clicking 
Save.
Setting the template of the website's root document
The website's root document has no parent from which the template could be inherited, so the first radio button option (No master page template) may instead be used if you wish to have an empty root page.
In most scenarios, it is highly recommended to assign an appropriate template to the root document and use content inheritance.
Additionally, the following actions may be used to manage the document's template:
•
Save as new template - saves the current template as a new re-usable page template. This can be useful if you wish to use an ad-hoc template for other pages.
•
Clone template as ad‑hoc - creates a copy of the current page template as a new ad-hoc template. This allows you to modify the design of the page without affecting other documents that use the original template.
•
Edit template properties - opens a new window where you can configure the properties of the currently assigned page template.
Inherit content
In this section, you can configure how the document should inherit content from its parent pages (if it is not a master page).
Select one of the following options:
Use page template settings
The inheritance is determined by the settings of the assigned page template.
To manage the template's configuration, click the Edit template properties button and set the Inherit content property on the General tab.
Do not inherit any content
The document does not inherit any content from parent documents in the content tree.
http://devnet.kentico.com/docs/7_0/devguide/index.html?content_management_overview.htm
Content tree that represents the site map of the website. It allows you to organize the site's structure or select a specific document for editing in the content section.
Inherit only master page
The document inherits content from the first master page above the document in the content tree.
If there are multiple master pages, the document only inherits from the closest one in the hierarchy.
Select inherited levels
You can select exactly from which parent documents the page should inherit via the checkboxes below.
The master page concept
http://devnet.kentico.com/docs/7_0/devguide/index.html?the_master_page_concept.htm
Master pages represent the powerful concept of sharing the same header and footer for all pages on the website.
It allows you to manage repeated items, such as the site logo, main menu and footer content in a single place.
The root of the content tree is always a master page. You can also configure any other page template to be a master page by enabling the Master page option on the General tab of the page template editing interface at Site Manager -> Development -> Page templates.
The following figure shows how the same master page is used for the home page and product page. As you can see, the pages are inserted inside the master page:
What is a page template
http://devnet.kentico.com/docs/7_0/devguide/index.html?what_is_a_page_template.htm
A page template is a predefined look for pages that allows content editors to enter the content.
A single template can be re-used for multiple pages with the same structure and design, but with different content.
Templates allow content editors to focus just on content editing, without the need to take care of page formatting.
They also help keep the web design consistent throughout the whole website.
The following figure shows how a single page template can be used for multiple pages: