my question describes it all actually. I wanted to know what is the difference between man and man 3 command to get the manual pages for unix commands?
UNIX command man pages are grouped in sections. See the section descriptions here.
General command line commands are in section 1. When you type man command, then man will give you the man page for command in the first section it finds it.
However, some commands may exist in more than one section. So if you have a shell command read and you type man read, you'll get the section 1 definition. But if you want the library call read, you would enter man 3 read which would tell man to go right to section 3 specifically.