gcode is what ultimately gets the printer to print, but they pretty much all use stl files. there are places like thingiverse who share stl files. you use the stl file in a program like cura or simplify3d with your machine settings to generate the gcode file. so if I had a gcode file for my printer it wouldn't work for your printer. but if I gave you the stl you can generate your own gcode.
I use several 3d printed parts in my tank.
I use several 3d printed parts in my tank.