Here you can setup the resolution depending on what you eventually want to do with your instructions.
You can choose between Dots Per Inch or Dots Per Centimeter. For printing on a normal home (inkjet) printer it is best to leave the DPI at 150. If you wish to publish or print on a professional printer (ie. a color laser printer) or printing press you can increase the DPI to 300. Note that the higher the DPI the larger your PDF becomes.
For publishing on a website as images you should use 72 DPI which is the standard screen resolution.