When you start with V5.99 you have the handicap that there are no tutorials for it written yet. But the concepts are mostly the same between V5.1.x and V5.99. V5.99 just has many more new features and ugly icons 
The root of a part in KiCad is the schematic symbol. This schematic symbol has an unique number assigned to it as an identifier (Called āTimestampā in KiCad V5.x and UUID in V5.99). But the number is not the reference, the schematic symbol is, and additional āfieldsā can be added to the schematic symbol.
Some of the schematic symbols are āatomicā / āfully specifiedā, which basically means that a footprint link (just a text string) is already assigned to the schematic symbol in the library. Other parts (such as resistors, capacitors, connectors and some more) are generic parts.
In practice it does not matter much. Using the same graphics for all resistors does make it trivial to update them if needed, but if they were in some library of parts then there probably will be tools to update graphics of many schematic symbols with some script.
If you prefer
Some people very much want a database driven approach. (And even do not consider KiCad a decent program without it). With such an database there are available / vetted / approved parts and these may already have ordering information, internal storage location, etc attached. KiCad does not do this (yet). There is some talk of implementing some database integration for KiCad V7, but that will be years.
The most up to date tutorials and background articles about specific features in KiCad is the FAQ Index which is also searchable, for example:
https://forum.kicad.info/search?q=library%20management%20category%3A19