To order a book, all you have to do is: 

1. Open the book you want to order and tap the shopping basket in the upper right corner:
   
   
   
2. Choose how many copies you want of each size by tapping the plus sign to the left of the book format you want to order:
   
   
   
3. Choose what paper type you want, Glossy or Silk matte paper:
   

If you want to add another book to the same order, tap "Add another product":

Then repeat the same procedure as above.