The musician has his music notation.
These notes are noted in chronological order on a line system.
The electronics engineer has his symbol font (notation).
Electronic symbols are wired in the circuit diagram.
At the very beginning the musician has a basic melody and the
electronics engineer a basic idea for a problem.
From this beginning arises a first version of the piece of music or the circuit is - on paper. In our time, we have replaced the paper with appropriate software (music notation program, ECAD).
Our composer will not write his orchestral piece in one step, but he will keep strumming on his piano to perfect his melody.
It's similar for the electronics technician. He has to go through the circuit in his head or play through it with a simulator. Components are added, removed, rewired or replaced by another variation.
Violin or viola?
Potentiometer or trimmer?
You will probably also test around with a plug-in board or in a small ensemble, if you are not Einstein or Mozart.
Now the composer is finished, but you still can't buy a concert ticket yet.
What's missing? Well... A hall with good acoustics, a conductor, many concert musicians, many instruments and please do not forget the chairs for the musicians! You don't want your first violin to sit on the floor.
So what are the "chairs" for the electronics engineer?
That's the footprint of a component!
A component manufacturer does not sell footprints, but rather components, but in the data sheet you will find a drawing of the optimum "chair" for the component. Your ECAD provides the footprint. In an ECAD, the footprint is often referred to as a package.
The concert hall with the good acoustics is the still empty board. The conductor must distribute and record his musicians appropriately.
As an electronics engineer (layouter), you must place the components appropriately on the board and convert the wiring into conductor paths (import).
The virtual board as layout and as 3D view in your ECAD. You have defined all placements and traces in the layout.
Now it goes on with ordering, production and assembly. But that's another story...