Hey Looking#,
Just to explain Kidalv's post apt-get is a command for installing/removing/updating/etc programs in Ubuntu (and several other Linux distributions). The package "apache2" is a web server, php5 is the interpreter for the web scripting language PHP, libapache2-mod-php5 tells apache how to use PHP, and mysql-server is a free SQL server. The most important thing about Kidalv's post is that it has nothing to do with running a file-server, mainly a web server.
The only thing that you need to run a file-server is a piece of software called Samba. It should come prepackaged with the server flavor of Ubuntu. If not, all you need to do is run the command "sudo apt-get install samba" apt will make sure you get all of the packages that samba needs as well as samba.
I'm sure you can find many tutorials on setting up shares with Samba, but here are a couple that I rounded up:
Samba Setup Guide Samba Configuration and Tutorial &
https://help.ubuntu.com/community/SettingUpSamba