Wouldn't it be wonderful if butter were always soft enough to use immediately? But softened butter takes time and energy, so take it out from the refrigerator a few hours before you need it and place it, unwrapped, in a mixing bowl. Use a flexible spatula to work it energetically.
If the butter remains hard, put it in the microwave oven for just a few seconds on low power, being careful not to melt it, or over a bain-marie. Finish softening it with the spatula or a whisk. In French, this is known as beurre pommade.