It is a decorative block that is used for decoration in the sides of the beds.
Go through this guide and follow step-by-step instructions to make a Cool Crate Design.
The first thing you will need to do is to place four spruce traps doors on the ground in the same way as shown in the image below.
After this, add four item frames in the middle empty cell and scaffolding on the item frames to complete the design.
Add two beds on the ground and cover the area around them with spruce trapdoors leaving two blocks on either side of the beds.
Add four items frames in the empty area and then use scaffolding on them. Do the same on the other corner of the bed.
Finally, place a flower pot on both crates and add red tulips in them.