I assume you mean you want to turn on syntax highlighting. The quick answer is typing ':syn on' while a file is loaded, and it should work automagically (you can put 'syn on' -- notice there's no ':' here -- on your ~/.vimrc file if you want vim to always turn it on automatically).
For a more detailed explanation, read the excellent vim documentation, it should be at /usr/share/vim/vimXX/doc (or type ':help syntax' on vim).
HTH
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