The two main parts of a template are the content management code and the theme. These should be kept separate so that the theme can easily be changed without affecting the structure. For example, the styles should be defined in an external style sheet and not embedded in the HTML code of the pages. The structure of a website will be defined by a set of templates. It is good practise to make the templates modular rather than having page templates containing all the code for each page. This allows site-wide changes to be easily applied. For example, the footer may be mostly identical between pages.
While making a site using web templates a person can make a base template file where it is possible to specify the non editable and editable regions separately. People also prefer the template based sites as they tend to be search engine friendly if the template is optimized properly. One can take the help of certain web site design software like Dream weaver for creating website templates easily. However, it also helps if one knows HTML to an extent.