When you cook you may come across terms that don't make much sense. The word "beat" usually means to strike something with an object. That's not what the word means in cooking. To beat means to rapidly stir a batter to thoroughly incorporate the ingredients along with air.
"Beat the egg yolks with the sugar until the mixture is doubled in size and lemon colored," or "Beat the butter and sugar together until the mixture is light and fluffy."
When you're cooking and baking, you need to understand terms and words and what they mean. Words have very specific meanings in the kitchen world. There is a difference between action words such as "beat", "stir", "whip" and "fold". They all mean something different in terms of how forcefully the mixture is manipulated. Another word that tells you to manipulate a dough is "knead."
Doughs and batters must be manipulated in certain ways to make the recipe successful. For instance, egg whites are "whipped" to incorporate air and stretch the egg proteins so they will hold air bubbles in a stable foam. But beaten egg whites are "folded" into a batter to help maintain the structure of the foam. And mixtures are "beaten" to mix them together thoroughly and to incorporate air for structure.
When a batter or dough is beaten, this is usually accomplished through a mixer, either a stand mixer or a hand mixer. You can beat by hand using a spoon, but this can take a lot of strength and energy. Beating with an appliance is a more efficient way to accomplish the task.