Hi, Balvir,
HTML is the primary language used to define a web page's contents. Every web page is written in HTML.
CSS is a secondary language which is used to specify how the contents are styled and displayed. Web pages don't have to use CSS, but a web page that doesn't use CSS will appear similar to a common text document, with default fonts and colors.
WebKit is the rendering engine built into Safari and some other browsers. Its job is to read HTML and CSS and properly display the web pages they define.
You don't need Xcode or Swift Playgrounds to make a web page, because HTML and CSS don't have to be compiled. You can even write a web page in TextEdit, save the file as an HTML file, and open it using Safari. Here's an example of a simple web page written in HTML:
<!DOCTYPE HTML>
<html>
<head>
<title>The best web page!</title>
</head>
<body>
<p>This is a great web page.</p>
</body>
</html>
I suggest searching for tutorials on writing your first web page. There are lots!