Computer-aided design (CAD) is the use of computers to aid in the creation, modification, analysis, or optimisation of a design.
3D printing is the construction of a three-dimensional object from a CAD model or a digital 3D model.
Electronics is the study of using various circuit components to make electronic circuits that perform a certain function or task. For example, we make a TV remote circuit which performs the function of changing the TV channels. Or we can make a circuit for flashing LEDs that turn ON and OFF the LEDs.