how does a 3d printer work?

How does a 3d printer work? After several decades of development, Now there are a variety of 3D printing technology process. From the categories divided into extrusion molding, granular material molding, photopolymerization and other moldings.The mail technical are Fused deposition modeling(FDM), Electron Beam Melting(EBM), Selective laser sintering (SLS), 3D platform (3DP), selective heat sintering (SHS), [...]