The printed parts: 1x lid, 1x left side, 1x right side and 2 holders;
2x M4 30mm+ screws to secure the holders;
1x 4mm 130mm axle to hold the lid in place;
Glue, to glue both sides together;
mount the holders in either side by inserting them in the slots and securing them with a M4 screw inserted at the back. The screw taps in the plastic on the front side of the slot, so be careful with drilling the holes. The holders are slightly asymmetrical, the thicker side needs to go on the outside so they will naturally fall outward.
Mount the axle in the lid, then mount the lid between both sides. Glue both sides together when everything fits nicely. After this, you can mount the toilet paper holder to the wall of your bathroom.