If a title is not available, you can place a hold.
Select "Place Hold" by the cover then tap on the red button, "Place Hold!"
After you place your 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 your 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.