After students sign in, they will have access to the features of Haiku Deck Pro- unlimited deck creation, privacy features, YouTube embedding, Zuru, and more. They can also add decks to the course gallery by following these steps.
The course gallery is private to the teacher until/unless a link to that gallery is shared. To get the link to the course gallery, refer to this article.
If you want your students to see the course gallery, you can share the link with them (or anyone else). Note that if you do share this link, the students will be able to see any decks that are posted to that gallery by other students in the course. If decks posted to the gallery are public and reusable (the default privacy setting), then anyone viewing those decks can make a copy of the deck to their own gallery.