Hi Sudhir,
Welcome to the group.
I assume that you have not worked on any test automation tool and are not aware of any programming language. (Good, if my assumption is wrong :))
First I will suggest you to begin with
Selenium IDE which is a record and replay tool available as firefox plugin. This will help you in understanding the element location strategy used by Selenium 1 and 2. Selenium IDE uses html kind of language to generate test scripts. You would also learn about "throw away" scripts which selenium IDE (or any other record and Replay tool) can generate for you. Once you realize that Selenium IDE can not be used to write maintenable tests then you should move to using more appropriate Selenium tool.
Since you are new to Selenium, can safely move to
Selenium 2 which is the most stable offering from Selenium. But before doing that you need to decide on the language you want to write your Selenium tests in. Java, C#, python etc.
You really don't need to master the entire language. You just need to know what you need to be able to work with Selenium. For example in case of java- core java is enough. Else sea is the limit.
Happy learning.
Lets us know how it goes.
~ seleniumtests.com