Demeter is one of the tweleve Olympian deities, sister to Zeus and daughter to Kronos and Rhea. Demeter is mother to the goddess Kore (also known as Persephone), Her daughter by Zeus.
Demeter is the goddess of crops, vegetation and motherhood. It is said that She gave the first wheat seeds to humans, teaching them how to cultivate the land and bake bread. She was honoured during the celebration of the Eluesian Mysteries.
The best known Demeter myth involves Her search for Her missing daughter Kore, who had been abducted by Hades with Zeus' permission. Demeter learned of the abduction from either Helios or Hecate, and left Olympus to wander the earth as an old woman. She removed Her gift of crops from mankind until Her daughter was returned.
When Demeter appears in your reading, She is telling you that you must exert you willpower. It is time to show off the skills that you have, but remember to do so in a controlled way that will benefit yourself and others. Think of Demeter giving the gift of crops and farming to others, and then discover how you can do something similar in your life.
When reversed, you are not using the skills you have either due to fear or anger. Perhaps someone has angered you, causing you to remove your expertise. Or maybe you are afraid of what the outcome may be. It might be best to withdraw for a short while, and then return to the situation and make use of all your skills.