Mechanical layers are also of interest. The mechanical layer (which may go under other names depending on the package) is used to provide an outline for your board, and other manufacturing instructions. It is not part of your actual PCB design, but is very useful to tell the PCB manufacturer how you want your board assembled. There are no hard and fast rules for this layer, use it however you like, just make sure you tell your PCB manufacturer.

When the PCB manufacturer fabricates the board, there will be alignment tolerances on the artwork film for each layer. This includes track, plane, silkscreen, solder mask, and drilling. If you don’t allow for this in your design, and make your tolerances too fine, you can end up in big trouble. Consult the manufacturer for what alignment tolerances they can achieve, and also what alignment tolerance you are paying for!

Finishing the board means also to create various reports and netlists in order to have a high-quality technical documentation. A netlist/wirelist, for instance, is essentially a list of connections ("nets") which correspond to your schematic. It also contains the list of components, component designators, component footprints and other information related to your schematic. The netlist file can be generated by your schematic package. Generating a netlist is also called "schematic capture".

The PCB package can then import this netlist file and do many things. It can automatically load all the required components onto your blank board. It can also assign a "net" name to each of your component pins. With nets assigned to your PCB components, it is now possible to Auto Route, do Design Rule Checking, and display component connectivity. This is the fundamental concept behind modern Schematic and PCB CAD packages.