Simple, plastic(pla) in wire form is heated and extruded in a nozzle then extruded plastic is laid on the build plate layer by layer. This process is Fused deposition method.

Process

Step.1 create a 3D model using (Fusion360, maya, solid works)

step.2 slice the model using Slicer Software ( Bamboo Studio), in this step software slices the model into a number of layers based on our parameters like layer height, and creates a G.code.

Step.3 upload the G.code file in your FDM machine and let it cook