Hi Aspirant

If you have any residential certificate or caste certificate of any state in India then you can see in it ,which category you belong to.

If there is no certificates and even it is not possible to make these certificates then you will have to register yourself as GENERAL.

If you belong to OBC category then it should be mentioned on certificate.If possible visit your nearby block office and ask them to make your certificates.They make ask you to show the papers of your parent's land/property for verification.

See the important thing is  if you dont have any certificate and you cannot make it through block office then you are GENERAL .

Hope this helps you.