The 3D feature is great for two things:
To view your pattern on a 3D product, click the 3D button
in the top bar:
When your window is small, you may only see the icon without the label:
When you are in 3D preview mode, you will see a Model selector
in the bottom right of the preview area. Click it to switch to another model:
Note that some of the 3D models are available to both Hobby and Pro plan, while others are exclusive to Pro plans (learn more about the plans on our Pricing page):