The story you are talking about is an old Cherokee tale called "Tale of Two Wolves." The wolves are symbolic, representing good and bad. The good wolf represents love, compassion, kindness, honesty. While the bad wolf represents hatred, jealousy, sorrow, and pride. When your teacher says the wolf who wins is the wolf you feed, they mean the wolf who wins is the one who you give into, the one who you give power over you. Give the bad wolf the power, you become the bad wolf. Give the good wolf the power, feed the good wolf, and the good wolf wins.