How to Place Any Item on a Block Surface
Placing a Single Item
Hold the item you want to display in your main hand and look at the face of the block where you want it to appear. Press the placement key (default P) while aiming at that face. The item leaves your hand and becomes a small decorative object attached to that surface, oriented to face outward from the block.
If nothing happens, the key is likely conflicting with another mod or a vanilla control. Open your controls menu and rebind the Plonk placement key to something unused, then try again.
Choosing the Right Face
You can attach items to any of the six sides of a block — top, bottom, and all four horizontal faces. Stand so the crosshair is clearly on the face you want; the item snaps to whichever face you are looking at. To place something on a ceiling or the underside of a block, look up at it from below.
Getting the Item Back
Left-click the placed item to break it and return it to your inventory. This works the same way as breaking a normal block, so you can reposition decorations freely without losing them.