[support] How to create a new template

[Roger]

Apologies for harping on with this problem, but I'm thinking, after so
much trouble with views-calc and computed field that maybe I need a
page.tpl.php or template.tpl.php with the appropriate php code to
display the correct information.
Problem is, some time ago I read a tut on creating a new
template.tpl.php, renaming it, etc but cannot find that tut nor how to
get the new template to display from a menu selection.

I really need some hand holding here to understand the process, where
the php code should be put in the tpl.php

Help gratefully appreciated
thanks in advance
Roger