"A FFF printer prints a 3-dimensional object by extruding a stream of heated or melted thermoplastic material, which is carefully positioned into layer upon layer, working from the bottom up. Just imagine a heated print head that is oozing out a permanent flow of molten plastic onto a surface in order to form, through multiple layers, the virtual object you chose to print. By adding layer upon layer, which will almost immediately harden upon leaving the hot print head, you will see the object that you chose to create materialize right in front of you. "
This is an excerpt of one of their articles. It breifly explains how a 3D printer works and what the result is. Here is a diagram of the process a 3D printer goes throughto prouce the final project.