You can find the Customization icon on the left side of the main screen—it looks like an artist's palette. Here, you can customize every item in your room, from the walls to the flooring, all the way to the windows and plants!

Tap the icon to enter the customization menu. Inside, at the bottom, you'll find all the items you can use or buy directly without going to the shop. Tap the piece of furniture you're interested in from the bottom menu to see it instantly in the room. Tap the tabs to switch item categories and pick your favorites. You can preview them in full screen by pressing and holding the corresponding icon.

Once you've chosen your furnishings, tap "Buy" or "Use" (if you already own them) to apply them to your room.