Using the Add→3D menu item
Use the 
button group in the Add→3D ribbon button group when editing the PCB.
1.Select either the top or bottom layer as the current layer.
2.Add your graphics.
3.Set the height and base of the graphic using the properties panel of the Edit 3D Object dialog that opens and click Done when finished.
See the example of adding a cylinder to the PCB below...
Adding a cylinder to a PCB using the 3D object tools from the Add→3D ribbon button Group