The first choice server os for the beginner I would recommend is the Linux Ubuntu LTS version for testing, and the server version for later when/if you want to optimize your server. You can find it on www.ubuntu.com under downloads.
If you are a little more advanced, I would choose Fedora Linux . Fedora is the development distribution that is built by an open source project sponsored by Red Hat. This software is from the beginning built to do what you want to do if you are looking for a server os. Any problem you will want to solve is easily fixed and you can change things yourself in the operating system because it is very easy to understand how Fedora Linux works, compared to Ubuntu Linux which is more automated. But with some cost in complexity, so Ubuntu Linux may be faster if you are not doing something "very advanced", then I would absolutely suggest Fedora Linux.
Someone not so experienced or well knowing might recommend you Linux Mint. This is not suited for server applications. Most likely you will end up with a lot of problems because of obsolete software here and there.