Ultimaker Cura is a slicing software which generates gcode files from stl files.
After downloading https://ultimaker.com/en/products/ultimaker-cura-software you might want to select your printer.
Load your stl file and click prepare to slice it.
e.g. the example file from our BlocksCAD page File:TrefoilKnotRemix5.stl has been sliced for Geeetech A10 as File:trefoilKnot5.gcode