I've always found manual pages to be of incalculable help to me.
The SECTIONS are some of the most important portions to me, especially NOTES, EXIT STATUS or RETURN VALUE, ERRORS, OPTIONS, as well as SYNOPSIS. SEE ALSO is typically very helpful.
I would note that manual pages are not just for command line commands, but also for library functions, for instance write(2) which is a C library function, as opposed to write(1) which is a command line tool that allows you to write information to a user.
For library functions, you also see the include files needed to allow use of that function in your application or driver, and you also learn if you need to link with a special library.
The -a argument and the -S # arguments are helpful:
Code:
$ man -a write // this will show all manual pages for write
$ man -S 1 write // this will show the man page for write(1), the command line utility
$ man -S 2 write // this will show the man page for write(2), the C library function
I also like the online site
linux.die.net which helps to find online manual pages.
What's most important is to really READ the content in the manual page. There are a ton of different points sometimes made about things and about other calls you may make. For instance the write(2) function talks about how you write to a file or descriptor, and the manual page also discusses what certain flags do when you use them in your open(2) call. And similarly, each of those types of functions' manual pages talks about the return value and the possible errors, which become very important the times when you open and then try to read from or write to a file and find that things aren't behaving.