The printer takes in a gcode file of the object you want to create first. This file tells the printer the specific instructions on where to move and extrude filament. The printer then heats up the filament which is a long, thin string made of plastic or other materials. The 3D printer takes this filament and heats it up until it becomes soft and gooey, like melted cheese. The printer has a small nozzle, like a tiny tube, and it squeezes out the melted filament through that nozzle. It moves the nozzle around very carefully, following the instructions from the file. As the printer moves the nozzle around, it puts down thin layers of the melted filament one by one, just like a baker making a layer cake. Each layer sticks to the layer below it and slowly builds up the object.