Hi @Rangaraj,
Thanks for asking this question. Head over to Eloquent JavaScript and download a free copy. Read it thoroughly and while you are reading think of something cool and start coding it in JavaScript.
You don't need to know everything to start creating JavaScript based apps. You just need to start doing things. If you are stuck somewhere, just google the problem or ask questions on devmag or forums like StackOverflow etc. After getting the basics cleared you can buy yourself a copy of JavaScript Good Parts to learn about best practices and other stuff. Here is a tutorial on HTTP and you can learn about AJAX here. There are numerous tutorials available on AJAX and HTTP. You just need to do a Google search to find out more such tutorials.
Once you are comfortable with JavaScript, you can probably learn a JavaScript framework like AngularJS, Backbone, Ember, React etc. But the bottom line is you can take your JavaScript skills to the next level only by practice.
Hope this helps!