Hello Sreeraj, 

For availing OBC Concession, you first need to have a Caste Certificate and also Caste Validity certificate. Along with this, you can avail OBC concession if you are a Non-creamy layer candidate, i.e. you should posses Non-creamy layer certificate. Apart from this, you should also produce annual income certificate of your father. If this income lies within the specified limits stated by the government then you can avail concession.

Hope this helps.