Cracking a CHAP from Freeradius

[undeath]

There is no easy and quick generic way to learn things like this. It's knowledge you amass over months and years by reading, observation and experience, combined with a fair amount of common sense.

In case of hashcat the wiki and forum are valuable resources. For generic knowledge about cryptography and computer science wikipedia is a nice place to start (although it may sometimes be too technical for a beginner).

Be curious and read articles about whatever seems interesting.