High Rise Shelf

Lay out the spacer positions on the back board and mark them. Glue the less-attractive face of each spacer to the back board and screw from behind through the back board so no heads show on the front — predrill the short blocks so they don't split. A brad nailer works here too.

Set each little shelf on its spacers, centered or offset as you like — lay them all out and eyeball the arrangement first — then screw them in place.

Sand and finish the shelf. To hang, screw through the front of a shelf into a wall stud where you can; where there's no stud, use a drywall anchor rated for the load. Level it, and it'll be far sturdier than it looks.