By default, the Header section of your Google Sites website consists of your Site Name and a site-specific search box. The Site Name serves as a link back to the designated landing page of your site which, by default, is the "Home" page. It is possible to modify the appearance of the header through the More Actions >> Manage this Site menu option.
The following modifications can be made to the Header section of your Google Sites website:
The Sidebar serves appears on each and every page of your Google Sites website. By default, it contains a Navigation gadget with links to your site's "Home" page and "Sitemap", as well as a brief listing of your site's recent activity.
Should you wish to modify the Sidebar - and it is certain that you will - simply click the Edit Sidebar link that appears immediately beneath the Sidebar. (You can also navigate to More Actions >> Manage this Site >> Site Layout.) In the sidebar section of the screen, you will have the ability to edit modify your Sidebar's content. Modification options include:
The Content area of your Google Sites website is where the bulk of your site's content will go. To populate this portion of your page, Google Sites provides a WYSIWYG (what you see is what you get) editor. You do not need to know any HTML (though some HTML is helpful) or other programming language to use it. Think of it as a Google Docs document, complete with a familiar looking toolbar with options to format text and insert images, tables, gadgets and countless other elements.
The Attachments section of your Google Sites website is a page-specific feature. This simply means that for each page, you have the option to enable or disable this feature. By using the Attachments option, you can quickly and easily add files (images, documents, ZIP archives, etc) to your page for quick access and reference.
Once files have been uploaded to the Attachments section of a page, you can safely hide the section via the More Actions >> Page Settings option should you choose. Direct links to files stored here will remain functional, but the list of attached files will not be visible to site visitors. This is something I've done with images on this very page.
Due to limitations inherent to the Insert >> Image feature the Google Sites editor, I recommend using the Attachments feature to upload any/all images to a specific web page. Doing this will enable you to remove the attached image when/if it is no longer needed. Once an image is added to the Attachments section, it will appear in the Insert >> Image dialog box for inclusion in your page. (A related article on working with Page Attachments, Images and File Cabinets discusses how you can also use the File Cabinet page template for a similar solution.)
Much like the Attachments feature outlined above, the Comments feature is page-specific. This feature can be used by Collaborators and Owners of your site to leave comments. Again, as this is page-specific, any comments left will only be viewable on the page on which they were left.
This feature is enabled on all pages by default, but can be disabled (hidden) through the More Actions >> Page Settings menu option.
The page Footer is a non-editable group of links that appears at the bottom of every page of every Google Sites website. It provides links to the following: