Unsalted Butter is typically used in baking because you can control the amount of salt that goes into the recipe. You can use salted butter if you prefer but you may have to adjust the amount of additional salt that is added. Because of the fat content in butter, margarine is not a suitable substitute for baking. Butter also helps you achieve a nice golden color to your baked goods.
To soften butter, set it out at room temperature for 30-45 minutes. To speed up the process, cut the butter into smaller pieces and allow it to come to room temperature. Microwaving butter is not ideal because it overheats and you’ll end up with half cold, half melted butter.