3D printing, also known as additive manufacturing (AM), refers to processes used to synthesize a three-dimensional object in which successive layers of material are formed under computer control to create an object.(Wikipedia) In order to make a 3d printing, you need to have a 3d printer and a software to make the model. Generally, you just design a model in a program, and then use the printer to print your work.
A 3d printer is like a regular printer. It makes 3d model a layer at a time. It starts from the bottom and goes to top repeatedly. It works automatically, but it takes a lot of time to print a object. The 3d printer does not need ink, it need some special plastic to print, such as ABS (Acrylonitrile Butadiene Styrene), PLA (Polylactic Acid) and PVA (Polyvinyl Alcohol).
There are many software to make 3d model. From my point of view, openSCAD is a good choice for beginner. It only has some basic tools and it’s not hard to learn.
Here is a photo of some 3d models that I made in my high school.