The reading stuff!
Instructions to get the distribution up and running and to use it.
The official Kali documentation is split into small sections and covers most of the topics you’re likely to bbe interested in, ranging from installing Kali to more advanced topics such as installing Docker in the distro. Kali offers an official training course that features a certificate on completion. There is a separate page with summaries of the included security tools with links to their respective pages.