Wish to do inter caste marriage. What's the method for court marriage?

Assuming you are Hindus,

It is better to marry with parents consent. You have not mentioned what is the girl age. Prohibition of Child Marriage Act states that a girl in India can't marry before the age of 18, and a boy before 21.

The parties have to file a Notice of Intended Marriage in the specified form to the Marriage Registrar of the district in which at least one of the parties to the marriage has resided for a period of not less than 30 days immediately preceding the date on which such notice is given.

The notice is then published/put-up by the Registrar of Marriage inviting objections, if any.

After the expiration of 30 days from the date on which notice of intended marriage has been published, the marriage may be solemnized unless it has been objected by any person.

The marriage may be solemnized at the specified Marriage Office.

Both parties along with three witnesses are required to be present on the date of registration/Solemnization.

In case you feel threatened for your security, then give a representation to the local SHO and SP for protection. Register a report if need be. In case you still don't get any recourse, then you may approach the High Court with an appropriate application for protection.