What is the Javascript

Javascript is a light-weight scripting language, not a high level programming language.
It is case sensitive, ( "JAVASCRIPT" and "Javascript" is not same )

we can write javascript codes on a HTML file inverted the <script>....</script> tags.

we can use a simple text editor like gedit (on linux), TextWrangler (on Mac) or notepad (on windows) to write javascript codes.

we do not want compile javascript codes before use it.

We use javascript on web pages and we use it to add interactivity to pages.

Javascript is not a relation of Oracle Java.
Javascript and Java are different languages.

First name of the javascript is ECMAScript and It has been changed as a marketing trick.

Javascript is a client side language and not a server side language.
Javascript is free to use, so we do not want purchase a license (like the linux not like the commercial windows)

Lots of browsers are supporting to Javascript, such as Mozilla Firefox, Google Chrome, Safari, Opera, and Internet Explorer...

What can we do with Javascript

we use javascript to validate a form data as a client side validation.
we can handle mouse events on web pages using javascript.
Google ads are related with javascript.

we can get the date and time from the client's PC with javascript.
we can detect the browser of the client with this language.

we can make online games, Image slide shows, simple animations, counters, converters, calculators, non stop pop-up windows, Drop down menus and many more using this scripting language.

How study Javascript

It is too simple.
You can study javascipt here step by step with related examples..
however you may have a basic knowledge about HTML.