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There are two types of files we need to create, Gerbers and NC Drill files. The gerber files define each layer of the board and the NC Drill files define all of the holes that need to be drilled. Combining them gives the fabricator the necessary information to create your PCB.
Gerber Files
Under "Fabrication Outputs", select "Add New Fabrication Output" and choose \[PCB Document] under the "Gerber Files" option. This will add a fabrication output for Gerber files corresponding to the PCB document in your project. If you have more than one PCB document, select the one you want to make Gerbers for from the menu.
Next, double click on the newly created output:
