Hey Aarti,
Javascript is kind of interpreted language, which is emited from server along with HTML and CSS. It runs on client side.
All browser has functionality by which it can understand the language.
tag in the HTML tells the browser that the next statemenet are script code rather than normal HTML until it hits .
For more details, you can check "Head First Javascript" or try
www.w3schools.com/js/default.asp[
^]
Hope that helps.
Milind