The sambar masala powder is basically used to make sambar (a famous South-Indian dal like curry). It can be eaten with snacks like idli, dosa or appe and even served for lunch or dinner along with steamed rice.
There are different kinds made like Idli sambar, udupi sambar etc. This masala powder is the main ingredient that adds aroma and taste to the dish. There are plenty of sambar powder recipes across South India prepared with varying ingredients. Most of these are made with coriander seeds, cumin and lentils as the base.