Basic Process

start a project. You start by editing a diagram, not the physical layout reality. That is called a schematic. the schematic is later converted into a physical layout.
Drag and drop components into the design
You must then connect them, and verify the design for connection errors.
Once you have the schematic, you can add physical reality to it. This consists of moving components around and rotating them in order to make the easiest connections, adding footprints for components and wire thicknesses. The footprints concept is that any component can come in various packages (or size/shape). We must specify exactly which package we are using.
Once we add packages and wires, we save the layout.
This layout can be converted to manufacturing files, for a CNC circuit mill such as OSE's D3D CNC Circuit Mill, or can be sent out for professional circuit board fabrication.

Videos

Playlist of 5 videos:

See Pieter Log for tutorial on building a DIY Arduino in KiCad, up to drilling/milling with D3D Universal. There is also a link to a tutorial video.
From Pieter Log - KiCad Tutorial for Arduino
From DIY Arduino - go to Minimalist Arduino, for the Minimalist_Arduino#Furthest_Simplification. 328 chip, crystal, 2 capacitors, and that is it for components. Let's do this as the absolute simplest worflow for designing the thing in KiCad, and then generating a CNC Drill File that can be run on the D3D Univesal. All as an exercise that someone can go through from zero to finish in one hour. That would be basic literacy in applied KiCad.
Online tool for gerber from KiCAD -> .gcode