Yum is the official package manager of Fedora Core. You can read the
Fedora tutorial on Yum. Apt is
deprecated for Fedora Core because it doesn't support multilib and isn't currently being maintained. There is a GUI for Yum called Yum Extender (yumex); you can download the old version for FC3
here; but it is not as efficient as the command-line Yum. I suggest you add the
Extras repository for additional software and possibly the
Livna repository for multimedia and proprietary software.