The slicer takes parameters about your printer, type of plastic in use, and other info to figure out how to slice the object in the STL into a number of slices. The output will use a standard format called GCode. GCode is the same standard used in CNC machines.
If you are not very experienced in Slicing Settings, you can just set the fields showed in the screen below and Authentise will use default settings according to your printer model.
If you have your own Settings file, you can upload it clicking on Choose file. It must be a .json or .ini file.
If you don't have your own Slicing Settings file but feel confident to edit ours, please download the attached templates, edit and upload it again in the Slicing Settings screen. Be sure to remember that Makerbots and Rep-rap based printers have entirely different file templates.