Once you've sign-in for the first time your will need to create your first project.
Hit the Create New Project button in the top left.
Give your project a name and hit Done. You will then see your new project on your dashboard.
Select your project and then choose one of two options :
Create a Scene - a scene is usually more than one object the together make an immersive experience
Edit 3D Models - use this to upload the 3D models of your products. You can add your 3D models to Scenes.