The key how additive manufacturing technology works is that parts are made by adding material in layers; each layer must have finite thickness.
Smaller the layer, greater the accuracy of the process is. Typing process flow of additive manufacturing is :

(i) Create 3D Part,
(ii) Convert in STL format,
(iii) Fed part to machine,
(iv) Set parameters of machine ,
(v) Convert geometric data in machine readable language,
(vi)  Start the process and
(vii) Post processing.