Follow the amounts of butter and sugar called for in the recipe you are making.
In the bowl of a stand mixer or with an electric hand mixer, combine the butter and sugar together.
The butter should be room temperature- not hard, right out of the fridge but also not melted. If you need to bring your butter to room temperature quickly, I suggest microwaving for 20 seconds on 50% power, turning over the butter and microwaving for an additional 10 seconds on 50% power.
Mix the butter and sugar together, scraping the sides periodically, for approx 2 minutes, or until the mixture has lightened in color and is fluffy in texture.
Proceed with the recipe you are following.