Essential Oils are 100% natural derived by plants, plant parts, stems, herbs etc. They can be distilled by various methods. They are just a one "note" scent, unless they are specifically blended. Depending on the purity, they can be used for therapeutic purposes. There are various grades of essential oils. Because they are 100% botanical, scent can vary. If they are pure, not diluted in a carrier oil, then depending on the application they should be diluted prior to placing on the skin. (This is what is officially suggested for most oils.) If they are used for natural perfume purposes, depending on the blend, they do not last long "scent" wise on the skin.
Carrier Oils are oils that help dilute essential oils so the can be applied to the skin directly. Carrier Oils include Carrier oils are often times vegetable or fruit oils such as coconut oil or avocado oil. These oils are usually extracted from seeds or nuts.