On a Linux box there are three places you can find more information about a command-line application:
root@kali-01: ~# nmap -h.
manand the application name on the command line. For example,
root@kali-01: ~# man rsyncgets you a pretty good explanation of how to use Rsync, the secure and logged file transfer protocol. Man pages are of varying quality and many of them are actually written by rocket scientists, so a newbie may have to ...