Mustard seeds have a sharp, pungent and spicy flavor. They come in three colors, black, brown and yellow. The yellow seeds are mildest in flavor intensifying in pungency as they darken.
Mustard seeds are an important part of Indian cuisine and are used across the country, featuring prominently in foods native to North, South, East and West India. Whole, black and brown seeds are most commonly used whole in Indian cooking. They are often added to a vaghaar (also known as tadka in Hindi and tempering in English). They form the flavor base for a wide variety of recipes from simple potatoes to dal to fish.
Cracked or split seeds, known in Gujarati as rai na kuria, make the base of tangy, spicy pickles (if you have not had an Indian mango pickle, I would urge you to do so. They are nothing like a dill pickle!)
In North India, mustard leaves are commonly eaten as well. In Bengali cuisine, mustard oil is the primary cooking oil.