I have explained it this way for years and is a simple method.
3D printing is like making pancakes.
If you make 1 it is flat and round, easy.
However if you make 100 more all exactly the same and stacked on top of one another you make a cylinder.
3D printing is no different.
A 3d model is generated in a 3d software program. This model is then split into hundreds of layers or cross sections. Each one of these cross sections is printed one on top of the other much like pancakes until you have a complete model.
In our process the cross sections are printed in a very fine powder which is held together by a specifically placed glue in the area of the cross section. The non glued powder supports the surrounding structure which allows you to make complex, interlocking* and mutiple parts all at the same time.
The unsued powder is then recycled to be used again which makes it an efficent system.
Now there are different types of printers using different materials and ways of processing though they all work on this same basic principle.