All together means everyone in a group: “We found the Guptas all together in the living room.”
Altogether, on the other hands, means to the whole extent; completely; entirely: “The factory was altogether destroyed by fire.”, “We were not altogether pleased by the outcome of the election.”
Usage example that uses these 2 words: The golf club factory was destroyed altogether in the fire but the owner declared that the golf clubs were all together in a safe place.
