A range of different technologies are in use by 3d Printers. What is shared across all 3d Printers is their basis in additive manufacturing. When producing a product, the manufacturer may start with a block of material and cut the object out of the content, or they may build a product by assembling it from raw materials. For example, when turning a baseball bat on a lathe, the manufacturer starts with a block of wood and cuts the shape of the bat out of wood. Alternatively, when creating a bookshelf, the manufacturer assembles the shelf from boards that they attach with glue, nails, or screws.
In additive manufacturing, products are created a layer at a time. Additive manufacturing is similar to building a house, where one layer of bricks is assembled on top of another.
The following video describes a range of 3d printer technologies, with names like FDM, SLA, MSLA, SLS, and Material Jetting, that produce products from filaments of plastic to fused metal.