Here is a couple of good threads on sand that might help you understand how it is used, where to get it and how it all works....
https://www.backyardchickens.com/t/444759/got-sand-you-should
https://www.backyardchickens.com/t/250190/anyone-use-sand-in-the-run-coop
https://www.backyardchickens.com/t/444759/got-sand-you-should
https://www.backyardchickens.com/t/250190/anyone-use-sand-in-the-run-coop