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Routing layers are used for component interconnects. These are the layers that designers spend the majority of their time perfecting. Routing layers can be located on both outer (referred to as top and bottom layers) and internal layers on your PCB. These layers must be provided to your fabricator to create your board. The image shown above is the top PCB layer so in addition to the component interconnect routing, you also see the pads for the actual components.

Ground planes and power planes are solid copper layers shorted to a fixed potential. Very simply, ground planes are connected to GND and power planes are connected to one of your onboard voltages. Similar to routing layers, these can be located on the top, bottom or within the internals of your board.

These planes may seem boring, but they are both highly convenient for distributing power and ground across all of your components and may greatly benefit performance under certain conditions. Fabrication files describing all planes within your design must be provided when creating your custom PCB. In the above image the green outline depicts the ground plane – which is to say that it is a solid copper pour over the whole layer.