There are four or five parts to the core funtionality of KiCad, depending on whether you count the small matter of annotation as a "part".
(Annotation is a "big deal", but it is handled so efficiently by KiCad… if you haven't done it for yourself… that you'll hardly notice it happening, and some would say it is hardly worthy to be an "equal" with the other "parts".)
(Words in bold also have entries in Encyclopedia… I will make them links in due course.)
- eeSchema: Draws schematic diagrams
- CvPcb: [\co1map Maps] schematic symbols to footprints. (If the annotation is imperfect when CvPcb is launched so that you will can perfect it)
- Netlist generation: In practice, a simple matter of button and one dialog. Does something complex and clever
- PcbNew: Draws [co1pcb PCB] artwork
When you start a new project, you will go through all of those parts, in that order.
Besides "the five parts", the better you understand the concepts of schematic symbols and footprints the better your KiCad work will go. After 5 years, I am still deepening my understanding, sigh. (Any other PCB design environment will have similar elements, although different environments may use different names for them.)