Linux is the name of the kernal, and therefore you have many different Operating Systems that can be installed on top.
Probably the easiest I've ever come across is the Ubuntu Server edition which can be placed onto a CD, DVD or Flash Drive. If you download the .ISO (OS File) from Ubuntu.com and then place it onto a medium which you can use.
Once the comuter boots up, select the boot menu (normally F12) and choose which option you want to boot from. From this, you should get a very nice wizard which shall guide you through the installation, however post back if you have any more questions.
Once you have it installed, it shall depend on what services you have running as to how you can configure it, for example if it is a web server then the chances are it is running Apache2 which shall require different configurations to a file server.
The most important things however are, lock down your file permissions, secure your firewall and don't be fooled by the common misconception that Linux based OS's cannot get viruses.
steps of installing and configuring servers in linux
Wow sorry that is way too generic. File server? NFS,AppleTalk,SMB,WebDAV,FTP,SFTP Web Server? Apache2, Lighthttpd,nginx If so do you need a database and php? If so with nxginx you may want to really look at how you are going to handle php. Then of course decide if you want to use postgresql,mysql, mairia ....
Print server? Voip phone? Ldap? .....
Is this for home and learning or is this for production? If it's for production do you need load balancing.......
You have lots and lots of options. For some the freedom is mind boggeling but if you know what the end goal is we can help you figure out options.