You have two good ways to fill muffin pans, depending on how uniformed you want to be. If you're not worried about being uniform, you can pour the batter from a mixing bowl with a lip. But, there's a good chance of that leaving you with muffins that aren't filled equally and won't bake equally. So, your better bet is to use an ice cream scoop to scoop your batter from the mixing bowl into the muffin pan. That will assure all your muffins are filled equally and will bake evenly.