If a title is not available, you can place a hold.
By the book cover, select "Place Hold" then tap on the red button, "Place Hold!"
After you place a hold, view your spot in line by going to your Shelf (book icon), next tap on Holds, then tapping Wait List ("2 weeks".)
You can view your place in line for a hold.
After you place a hold, go to Shelf > Holds and tap the Clock icon or the "2 weeks." You'll see your approximate wait time, the number of copies in use, and the number of people waiting.