If you learn nothing else about Mockup 3D, learn this.
Pick a model. Select "create scene" and name it. You need to sign up to do this.
When the model has loaded, upload any image (psd, png or jpeg) by dragging the file onto the dashed box marked "add image".
The images panel will expand and your image will be selected on the right. Move it by dragging.
Hide, show, rotate and do many things the layers
Change the shape of the model using the shapes panel below
Click and drag the model to rotate it in 3D
Export an image by hitting the big red button or the E key
Share a 3D link like this by going to the "File" menu and clicking "Share".
More detail in this video: