Each shelf prints in 4 parts; one top, one bottom and two pins. The parts are a relatively tight fit, so some small post processing to trim off any elephants foot from the top is useful.
Steps to fit:

• Slide the top into the grooves of the bottom.
• Mount to where you'd like it on the daybed.
• Push the parts together firmly so that the holes line up.
• Press the pins into the holes.