Subas,
First pick your client bindings flavor. It can be Java or C# or Python or NodeJS. This is the first important job. Since you say you are in a QA job already, you might want to see what is the technology stack your development is using. If they are using Java, you can consider focussing on using Java as the programming language in which you will write automation tests.
You would also need to ensure that your HTML basics are very strong and you also know a little bit of Javascript as well.
You also need to spend a bit of time understanding location strategies that rely on XPath and CSS.
Once you have figured out all the "pre-requisites", I would suggest that you spend some time on learning and understanding what each of the different APIs that selenium offers, actually does and how to use them.
You can start off with trying to use the Selenium IDE [ I have not tried using it off-late so I don't know its current state ]. There are a lot of tutorials/blogs that people have written that help you get started with Selenium.
Also spending time learning a TestRunner [ In the Java world it would either by JUnit or TestNG ] will benefit you additionally.
Hope that helps you get started.