There are millions of different schematic symbols and PCB footprints, and KiCad “only” has libraries for about 20.000 or so.
KiCad does have pretty good editors for creating both schematic symbols and PCB footprints.
The FAQ part of this website is a good starting point for text based tutorials on many aspects of KiCad. It has much more information than an “average faq”. It has some 80+ articles and tutorials that go quite in depth into the details of how KiCad works.
Some people like websites such as snapeda and samacsys. These (and other) websites have immensely big libraries with schematic symbols and footprints, but the output is usually generated from an internal database and some exporter script, and the quality of those exports may vary.
Even if you want to use such websites, I still believe that learning to work with KiCad’s own schematic symbol editor and footprint editor are essential skills. There will always be parts that are not in any library, or have to be adopted to special needs. The editors are quite simple to use. Their GUI’s are very similar to the rest of KiCad.