Whether you're making brownies from scratch or whipping up some boxed ones, your recipe is going to call for some type of fat - either oil or butter. Olive oil will add a pleasant bitter tang to the brownies as well as a fruity touch, while vegetable oil yields a plain flavor. Coconut oil is also nice to use with brownie mix, especially if you want that delicate aroma of coconut in the resulting brownies. There are other options besides, such as avocado or Greek yogurt, but if you're new to baking you'll probably want to master the classic recipe before experimenting.