This is Fedora you are using.
On fedora yum
command is used.
yum install <package_name>
yum install postfix
And you're using old Fedora which doesn't have support now.
You should use latest Fedora, i.e., Fedora 19 Code name: Schrodinger's Cat
released on 2nd July 2013.
You can also use Fedora 17 or 18, still the support is available for them.