Amit, the metabolic job of carnitine is to transport fats (technically, fatty acids) into intra-cellular organelles called mitochondria. When fatty acids arrive in mitochondria they are "burned" to produce metabolic energy (ATP) - the fancy term for this is fatty acid oxidation.

Because you are hoping to lose weight by using your fat stores as an energy source and also because you are a vegan you could well be deficient in carnitine (animal foods are the best sources of it).

With the disclaimer that I am not a medical doctor, taking 250 mg of carnitine regularly sounds OK to me.