No single Wiccan answer
Ask ten Wiccans what magic is and you will get a spread of answers. Literal: an actual force or influence that practice can direct. Will and intention: a way of concentrating purpose so that you act differently afterwards. Psychological and symbolic: ritual as a way of working on yourself, with no external claim attached. Mixed: most people, most of the time. Pretty Little Wiccan teaches the practice and describes the interpretations. It does not tell you which one is true.
What we will not say
You will read that magic works by raising your vibration, aligning frequencies, or through quantum physics. Those are modern rhetorical borrowings, not established mechanisms, and the physics ones are simply wrong. We would rather say we don't know.
A common definition
Aleister Crowley's much-quoted definition, magic as the art of causing change in conformity with will, reached Wicca through the ceremonial magic tradition that shaped it. Dion Fortune's version, change in consciousness, is quoted just as often and points somewhere quite different. Both are twentieth-century occultist definitions, not ancient ones.
Magic is not a substitute
This is the firm line. Magic does not replace medical treatment, legal advice, safeguarding, emergency services, therapy, or a difficult conversation. Do the real-world thing first. A spell alongside it is fine; a spell instead of it is not, and any teacher who suggests otherwise is dangerous rather than advanced.
Results, honestly recorded
Write down what you did and what you noticed, not what you hoped. Coincidence, selective memory and wishful reading are ordinary human features, and a practice that keeps proper records is more interesting than one that keeps score.