Merlyn's magic makes it seem like Wart is spending many days with the geese, even though it really only takes place for one night.
Lyo-lyok explains the social structure of the geese to Wart. They are a highly individualistic species without kings or laws. They have no concept of territory, except in the case of the nest—which is considered private property.
She also explains a lot about the custom of migration, how it probably got its start, and how new admirals get chosen when the old ones die.
The Wart learns a number of songs the geese sing as they are flying: silly songs, sentimental ones, and heroic ones.
The geese stop at several islands on their way across the North Sea, and finally they make it to their destination. Their migration is over. They flew all that way—and boy are their wings tired. Literally.
When Wart wakes up the next morning, Sir Kay accuses him of snoring like a goose honking.