Thanks for your question.
To start with you will need to track the poster to the experience. We have a good video which explains what makes a good tracking image, so be sure to check that out.
You will have to create/download and export the 3D models you would like in the experience using an external 3D software, making sure that they are a supported format for Studio.
You would then import the models into ZapWorks Studio and position them on the tracking image relative to how you would like them to be viewed in the experience. Examples and helpful documentation on 3D models can be found here - 3D Models.
If you would like the models to be moving - either animations that are pre rendered or just the position in the scene, please have a look at the video on timelines to find out how this can be done!
Hope this helps, we are looking forward to seeing what you can create!