you can apply the oil however. When you apply the oil in your skincare routibe depends on the type of moisturizer you use. if you use an oil free moisturizer then you will apply the oil AFTER your moisturizer. If your moisturizer is NOT oil free, then apply the oil BEFORE moisturizer.
There are lots of benefits of using an oil, mainly to give an extra boost in hydration for your skin. It is very versatile. You can mix it in with your moisturizer, foundation etc. another way to use the oil is to add a few drops in the dip brow when it starts drying up. That way it moistens the product and it will become good as new!