Multilayer
Imagine a multilayer PCB as a sandwich made out of two or more double sided PCBs glued over each other. As a result you have inner layers, which can be used for signals. You can set vias to connect the inner layers (buried vias) or vias to connect outer and inner layers (blind vias).
See the sketch of a 16 times multilayer showing the principle of a through hole, a blind and a buried via:
For a 4 times multilayer set the function of layers 10 and 13 from "Other" to "Copper inside". If you need more layers, please set further layer functions to "Copper inside". You can rearrange the whole set of layers.
If you wish to use blind vias (expensive) and buried vias (more expensive), you must define Padstacks in Menu Actions / "Define Vias as PadStacks". Now you are able to use further vias upon layer 101 ff. On Layer 100 those vias are defined, which contact all copper layers.
If you press key [.] in "Draw track" mode (as if to set a normal via) and then key [o] for "Options" then configurate several vias in the "Via-Options"dialog on to the buttons on the right edge of the dialog. Use button "PadStacks". Those buttons later appear also beneath the layer tool for a quick selection while placing tracks.
If you need further information on the capabilities of multilayer technique, please contact also your PCB manufacturer. Sure they can provide information on their multilayer processes.
This TARGET 3001! project has a multilayer configuration: File:Pic 4Multilayer.T3001
In 3D view you easily can see the separate tracks upon separate layers (though it's a bit difficult to figure it out in this 2D screenshot):
