Custom module and template.tpl.php files I am just getting started with custom modules for my test site on my localhost. Is there a simple demonstration online where there is an example of using a mymodule.tpl.php files to render my content? 

At the moment I have create a hook_menu() function also a function for the page call, all it does is return some text.
There are a lot of examples of use of the Drupal API for module developers in the Drupal documentation. In particular, you may find the Examples for Developers module handy, especially the "theming_example" sub-module. This is not an actually functional module, but just a container for a lot of example code that new developers can test, manipulate and learn from.