Currently there are several different methods of 3D printing, below is a brief description and link to a video of each type.

One technology is Selective Laser Sintering which uses high powered lasers to fuse small particles of material together and into 3D shapes.

Another Technology is Stereolithography known more commonly as SLA. This technology uses a vat of UV curable resin that is hardened layer by layer with ultraviolet light tracing the pattern of the object to printed solidifying the resin along the way.

The first two are primarily used in commercial printer, however the last technology is seen in both commercial and desktop 3D printer applications.Fused filament fabrication (FFF) or more commonly FDM or Fused Deposition Modeling (Stratsys Inc trademarked terminology), uses long printing filament that looks similar to what you would find attached you your weed whacker. This filament is heated and fed through a nozzle and material is added layer upon layer until the object has been made.

For the purpose of this site I will be focusing on personal printing which is primarily dominated by filament style printers.