1. What codes are you trying to add? CSS? If so, you would use Simple CSS.
2. As in how to add header images to your categories? CSS won’t work for that. You’ll have to use PHP with GP Hooks or your functions file.
3. Not sure what you mean here? If your page was titled no-title it means you didn’t add a title to the page when adding it (the big textbox at the top of the add new/edit page area).