The word Wiccan used as a noun refers to an individual that belongs to the religion Wicca. As an adjective, the word Wiccan is used to describe anything relating to Wicca. For example, a Wiccan ritual, a Wiccan altar, a Wiccan esbat, a Wiccan Sabbat, the Wiccan Wheel of the Year. Wicca itself is occasionally described as “the Wiccan religion”.
For an exceptionally redundant example: “Stacy is a Wiccan, she discovered Wicca 10 years ago and joined our Wiccan coven last month.”