"Man pages can be limited, and they're often not great if you're an absolute beginner, especially if the command is a complicated one. But they are often enough to get you started -- and in some cases they can quite genuinely provide an entire manual. Check out man bash for a very comprehensive example.
One point to bear in mind is that there can be multiple categories of man page. The ones you are most likely to run across are:
"1 Executable programs or shell commands
5 File formats and conventions eg /etc/passwd
8 System administration commands (usually only for root)"
