Some ideas:
- Start with a book - something like Gast's 802.11 Wireless Networks
- Some good websites exist, too, such as this one.
- There are some wifi sessions from Sharkfest over the years. Youtube has many of them: https://www.youtube.com/c/SharkFestWiresharkDeveloperandUserConference/videos.
- The 802.11 specification is there, too, but it is a large document. Recommended only for advanced users.
- wi-fi.org has some good information, too, if you dig.
This is just a start - there are other books and certification programs that you could study for that provide knowledge. Good luck!
