How do they write down the movements for ballet dancers to perform?
How do the Enchanted Mice know when to twirly-twirly and not bump into the Queen of the Chickens or the Prince of Tractors?
There are various systems that have been developed over the years. There are even archives specifically for choreography. One that I remember from college was Laban Notation aka Labanotation.
There was also a Slate article about this a while back.
Actually, they know because their choreographer/dance director tells them what the choreography is. AFAIK, nobody ever gives the dancers a photocopy of the written Laban notation, and says, “Here, learn these steps!” The dance director would read it, and then teach it to them.