Head tags can be added to the theme as a whole or can be added for certain page types.
For example you would want to add your Google Analytics scripts to your whole theme to track every page. But you may have specific scripts or styles (or anything that goes in head tags) that you want to have only on Product Pages.
To add theme wide head tags simply click the Head Tags link from the Themes accordion section (the main section) You will be presented with an HTML editor to add any head tags to.
This section is rendered into your template using the $$HEADTAGS$$ mergecode. This should not need to be modified.
Adding To Head Tags for a Specific Page Type
To add page type specific head tags you can add a special tag called an <ac:templateoverridearea id="UniqueId"></ac:templateoverridearea> with a unique ID (this can be anything).
Then add the same tag to the page type that you want the specific head tags on.
The following HTML outputs are from the Homepage and the Product Details page.