MODx templates are not like those of other CMSs. A template is simply the HTML you would use in an ordinary .html file, with the dynamic parts (menus and individual page content, for example) inserted by means of MODx tags.
You'll need to learn to understand how to use snippets (for PHP code, used for menus and news or blog listings, among other things), chunks (chunks of commonly used HTML code, frequently used for footer content) and Template Variables (TVs, probably the most powerful features of the MODx templating system.
There are a number of tutorials and articles about templates; here's one
https://forums.modx.com/thread/18244/tutorial-for-creating-a-template-with-revolution