There is not much spicy food in Russia. Usually, people just add fresh garlic or onions to their meals. But be careful, homemade spicy mustard is as spicy as Japanese wasabi. Usually spicy mustard is served as a sauce for lard or meat jelly. Some people who like a lot of spicy put mustard on a piece of bread.
Try just a little bit in the beginning. Because if used too much it may hurt a lot. Sometimes people even cry and become and have a red face.
Usually, 1 tablespoon is enough for several people. The potency of mustard is defined by its freshness. If mustard is purchased in the shop it will never be as spicy as fresh homemade.