All the decorations at the store are divided between tabs that correspond to different areas in the game 🌳 To unlock a tab, you need to open a new area.

To unlock decorations for the areas that are already open, you need to beat match-3 levels. The required number of levels to do that is shown under each decoration in the store. 🌸

Remember that pathways can only be placed in the areas where they originally appeared, but all other decorations can be placed in any open spot.