create a new package (which will be empty), find where it is located, look at the dir structure.
All templated pages in openacs have at minimum two files, something.tcl (code establishing data sources go here) and something.adp (html and data source rendering go here).
Create one page that creates one constant string variable, render that variable on the page, try with and without master template. An example of this is in the templating system demo.
FOR DETAILS, see templating system docs and templating system demo.