You can enter a Design Challenge if it is listed in the Live Challenges page.

Tap the image to read the event details, see the requirements, and view the prizes.

Tap "Enter Challenge" to create your design. 

Once you're in the Challenge, you will be shown the requirements for that Challenge (if you are entering a Daily Challenge, there are no requirements). Items in the blue bubbles are required items while the items in the purple bubbles are optional.

After you have tapped on a requirement filter or furniture bubble to begin selecting items, you can tap the search bar or magnifying glass to add filters such as brand, material, and color to further refine your search.

Once you have completed your design with all the blue bubbles furnished and have met the requirements to enter the Challenge, you will see the "Finish" button turn green. Tap "Finish" for one more chance to review the event details, and then tap on "Submit Design" to submit your final design.