WordPress blog designed to give the blog owner the ability to control and assign what users can and cannot do in the blog. A blog owner can manage and allow access to such functions as writing and editing posts, creating Pages, defining links, creating categories, moderating comments, managing plugins, managing themes, and managing other users.
What is the appearance modifications?
When I say appearance it means styling so CSS basically modifies typography and colors.
CSS allow to make style changes on the theme.
What you can change by editing a theme’s CSS?
Font size and colors ( header size and color )
Styling font such as drop shadow effect, emboss look, drop caps, etc.
Changing background/border colors
Changing background image, adding image, removing image
Changing navigation button color
Changing side bar, main page, footer or header/banner area colors
Structure of the WordPress Blog
Actions are triggered by specific events that take place in WordPress, such as publishing a post, changing themes, or displaying a page of the admin panel. A plugin can respond to the event by executing a PHP function.
When a PHP function executes, a certain event occurs on the blog.
Such as when you click on a navigation button, it opens a certain page in the blog, that is a function. Just like using a contact form is a function too.
WordPress blog provides a total separation between style and content. This means that, all the pages and post contents are contained in a MySQL database, all the files that decide what the site looks like and how the site functions are contained in a WordPress Theme.
WordPress uses various template files to put together almost like a patchwork of different files to create a full page. For example, when you open a WordPress site in a browser, you will see the index.php page. The WordPress template actually creates that page with header.php, sidebar.php and footer.php in addition to its own content.
To change the look of the blog ( in a particular theme ), you edit the CSS.
To change functionality of a WordPress site, you write PHP codes, and also can be done by adding WordPress plug-ins.
If this explanation is too difficult to understand, I can use a car metaphor.
Think about a WordPress blog like a car. Your car can be red, or blue, and have tinted windows. These are all styling.
How fast your car goes, if the car has 5 gear, or uses electric or gas are the functionality of the car.