How do I create new content type with editable fields? I want to create another content type similar to the basic page. I've designed a simple html layout with a block of copy on the left hand side and an image with a caption floated next to it on the right hand side.

I want to be able to add this as a template to the Drupal UI so that a user can pick this template and enter their copy, choose/upload an image, enter an image caption and possibly show a widget below the content based on what the page is about.

How would I go about configuring this so I can add this page template as a content type into the Drupal UI?
Based upon the mentioned requirement, to me it seems either of the following situations:

For Drupal 7:


Theming the node add page: page--node--add--[content type].tpl.php
Theming the node edit page: page--node--edit--[content type].tpl.php


For Drupal 6:


Theming the node add page: page-node-add-[content type].tpl.php
Theming the node edit page: page-node-edit-[content type].tpl.php


More info about the same you can get from here:
https://drupal.org/node/1092122
https://drupal.org/node/1089656
https://api.drupal.org/api/drupal/modules%21system%21page.tpl.php/7