Firstly, are you planning to have a moving cart or food truck, or is it going to be in one place? If it's a moving cart, things would be much easier for you. Officially, to be able to sell food, you should have a FSSAI licence. Then, the food inspector from the BBMP local office would visit from time to time to check hygiene, food quality, and cleanliness.
Unfortunately, in India, this is not enough! You would have to bribe the policemen and local goons and maybe even have beef with the neighbouring stall owners.
It is better to start with a very small menu like bread-omelette, vada pao, or maggie. Gradually increase the menu as per the local preferences and taste of your customers.
Invest in a clean and attractive stall so that you may be able to attract young customers. It would also help in building a loyal customer base.
There is not much to do officially, but unofficially, you would have to be prepared for absolutely anything. Hopefully, you will be able to get a good repo with the police men. Good luck with your stall.