After choosing the 3D view for the first time by choosing 3D in the tab bar after opening a document will generate a 3D representation of your board. Please note: Complicated and large PCBs will take some time until the 3D view has been generated. Just be patient.
Copper will create the PCB outline and extract to a board width of 1.6mm. Copper will also create solder paste indicated by the tCream and bCream layer and generates a silk screen composed of tNames and tValues for the top layer and bNames and nValues for the bottom layer.
Please note: Copper will only show layers in 3D that are set visible in the layer inspector.
Navigating in the 3D view
By panning with one finger you orbit around the PCB. Use two fingers to move the camera around relativ to the current view direction and pinch with two fingers to zoom in and out. Using this simple navigation scheme you can adjust the camera position to any angle and position you like and inspect the board in great detail.
This can be very useful to find issues before you get the board soldered. In one of my layouts I had a small touch button very close to a pin header strip. In 3D view I realized that it would be very uncomfortable to use that button in this configuration. In typical PCB layout I didn't see that as an issue.
Tapping on this button will bring up the presets selection. Presets store the camera angle and scene settings so you can restore them quickly for a customer presentation or if you want to store them for later use. More on this topic here.
Default camera positions
Tap on this icon to choose from standard camera positions like Top, Front or Isometric (Home).
You can adjust various parameters of the 3D view like light settings, solder mask and floor materials. More on this topic here: Scene inspector.