HTML templates are used to define the layout of all Help+Manual's HTML-based output formats (HTML Help, WebHelp, eBooks and Visual Studio Help). In topic pages, what you enter in the editor defines the content, the templates define the framework in which your content is presented. The HTML templates are stored together with your project.
The same HTML topic page templates are used for the topic pages in all three formats. In addition to this there are also separate templates for the frameset file and the Table of Contents and Keyword Index frames used in WebHelp, where they emulate the HTML Help viewer user interface.
For normal work with Help+Manual you don't have to think about what HTML templates contain and how to edit them. That is all handled in the background by the program. A simple style editor is provided that allows you to modify the basic layout of your pages in the associated output formats without having to edit the HTML code directly.
Nowadays you will almost always choose an HTML skin to publish your project to WebHelp or HTML Help/CHM. A skin is a special kind of Help+Manual project without topics that only stores your HTML templates and all the settings relevant for HTML output to these two formats. When you choose a skin, the templates and settings in the skin completely replace those in your project.
Normally, a skin is pre-designed and you don't need to change anything. However, if you do want to change something, you must do all your editing in the .hmskin skin file. Editing in your Help+Manual project won't have any effect because those templates and settings are not used.
To edit a skin, make a copy of the .hmskin skin file in your project folder and then open it in Help+Manual by selecting .hmskin as the file type to open in the Open dialog. All the templates and settings are in the same places as in a normal Help+Manual project.
Exception: HTML Export Options
The HTML Export Options section is not stored in skins and needs to be edited in your project.