You probably had to checkmark to install a Desktop Environment when you installed. Since you did not, you can probably install it at the commandline:
sudo yum install gnome-desktop
But you can of course try the larger iso if you've already deleted/re-started.
Since you sound like a true ground-zero beginner, i will share this: I have find that beginner's often need to start with distros that are almost fully pre-configured. Xubuntu, LinuxMint XFCE, or Fedora or my recommendations for beginners.
RedHat, CentOS, Fedora are of one Family. If you want this family, I recommend Fedora for a Desktop.
Ubuntu, Mint, Debian are of another Family. If you want this family I recommend LinuxMint XFCE.
Your freind has recommended CentOS. CentOS is a great stable distro, binary compatible with RedHat Enterprise Linux. However, i find it is best suited to server, because there is much less desktop pre-configuration. Things often don't "just work". For that reason you should consider my above recommendations.
Also you should note that graphics especially 3D graphics & compositing will not work so well or or maybe not at all in a Virtual Machine.
Using a linux in a virtual machine is a great start, but when you are ready for fancy graphics or games, you'll need to graduate to a physical machine.