To participate in a challenge, you must place the necessary furniture. Click on the colored bubbles to do this. By clicking on a bubble, you will discover the choice of the item you own, and below the items you can buy. Blue circles are required; purple (plants, pictures, vases, etc.) is optional.
You can only participate in an event if all objects place in blue bubbles. You cannot choose where to put things, only what items to use. For example, most challenges have limits, "Three green elements" or "A ceramic clay table." The only challenge without specific instructions is the daily challenge, in which players cannot participate.