So in short, how do essential oils and carrier oils differ?
Carrier oil tends to be extracted from nuts, seeds or fruit through cold processing / pressing. *Emu oil being our exception! They tend not to have any smell, or only a very slight smell, and are quite thick in consistency.
Essential oils tend to be extracted from plants or shrubs through distillation (water or steam usually). The parts of the plant might include: roots, bark, stems, leaves, flowers. Essential oils tend to be very aromatic, and are much thinner than Carrier oils in their consistency.
But we rarely use one without the other because they are a bit like peas in a pod!