ENGINEERING is the process of analyzing a problem and determining what physical properties are needed for any potential solution.  For example, with a ball shooter, if you know how high and far the ball has to go, you can calculate the required speed and angle for launching it.  These are properties independent of any particular solution.  If you then want to use a flywheel to shoot the ball, and you know the mass of the ball, you can then calculate required the speed and rotational inertial of the flywheel and also the required motor torque and speed.

 

DESIGN is the process of deciding exactly how your proposed solution will be constructed.  In the shooter example, this would include designing mounting brackets for the motors, designing the flywheels, how they attach to the motor shafts, etc.  This is very detailed work, down to the location of every screw hole and every dimension.  The resulting design is a CAD model or a set of detailed drawings.

 

FABRICATION is the process of taking the CAD design or detailed drawings and actually producing the parts.  This may be done with CNC machining, laser cutting, 3D printing, etc. Fabrication also involves assembling the parts into the finished device.  This is a non-trivial step that tends to be underestimated. The tendency is to think that everything will just go together like Lego blocks.  But with a bunch of hand build parts, nothing goes together smoothly and you have to recognize when parts need re-working.