1) Browser and URL

Browser

A browser is must to open any website. Browser plays a major role in opening the any website.

Browser will understand only the languages like

HTML

CSS

JAVASCRIPT etc.

Uniform Resource Locator(URL)

It is the address of the website

For Example:

2) Syntax

Rules of language. Misssing any of the details will change the appearance of the page.

Syntax is not the program, it is the part of the program.

<!DOCTYPE html>
<html>
<head>
<style>
body {
  background-image: url('images/mountain.jpeg');
  background-attachment: fixed;
  background-size: cover;  
} 


</head>
<body>

<h1>Hii</h1>

</body>
</html>

In the above example there is a missing closing style(</style>) so the appearance of the page changes.

<!DOCTYPE html>
<html>
<head>
<style>
body {
  background-image: url('images/mountain.jpeg');
  background-attachment: fixed;
  background-size: cover; 
}  

</style>
</head>
<body>

<h1>Hii</h1>

</body>
</html>