Mace is not a spice all its own. It actually is part of a nutmeg kernel. The waxy outer coating on the nutmeg seed kernel is collected and processed separately to produce a milder, sweeter version of nutmeg.
Whole mace pieces are known as blades and like nutmeg, are better left whole and ground as needed. Mace is usually added at the end of cooking right before serving. Blades can be left whole to season soups or curries for example but like bay leaves, need to be removed before serving.
You can substitute mace for nutmeg in recipes to gently lighten the flavor with the same results in taste.
Mace is often found as a balance ingredient in pickling spices.
Mace partners well with other warm spices like cinnamon, cloves, ginger or cardamom.