Your design challenges are on your dashboard. To get to your dashboard, select your username in the top right corner and then My Dashboard:
On your dashboard, the My Challenges tab shows you your Active challenges:
When you start building a design challenge, it will show up here. Your project will stay in Active while you work on it and post pictures and videos to your engineering design process.
After you make a Reflect post, your project will move to the Completed tab, where you can still access all of your work:
If you're part of a membership, you will also see a tab with your membership design challenges: