How to make changes in HTML code and make them show up on site
Look into using the Features module. This way, you can convert any configurations that are stored in the database to code, push them up to the repository, and then pull and revert all the features on your test and production site. You can add template work as a custom feature as well. You should stray away from editing code in Drupal and lean toward creating custom themes, modules and features. I would be no where without this module.