Vegetable oils are triglycerides that are extracted from plants. Vegetable oils can be used in a variety of culinary applications. It is most commonly used in frying as a medium for evenly distributing heat, but it also acts as a shortening agent by inhibiting gluten formation, to impart mouthfeel or moisture to baked goods, for its flavor, and to extract flavors from oil soluble compounds.
These oils can also be partially hydrogenated to create solid fats such as margarine or Crisco. Hydrogenation creates a solid fat by decreasing the amount of cis-double bonds. These double bonds decrease the amount of van der Waals forces by creating less linear molecular configurations, which reduces the amount of contact between the triglycerides and results in less stability. Hydrogenation removes these elements causing an increase in intermolecular attraction and stability.
Oils are 100% fat, so it is important to release that they increase they contribute more calories to a food than proteins or carbohydrates.