Both PHP and MySQL come with FC3, so you may already have them installed (though they are not the most current versions). You can check with
Code:
$ rpm -q mysql
$ rpm -q php
If you have MySQL, you can start it with
Code:
# /etc/init.d/mysqld start
If one or neither of these packages are installed, you can install them with your Fedora installation discs and
system-config-packages.
As for yum, I strongly suggest checking the
FAQ on how to set it up (note: link is for FC3).