Free and Open Source Software.
Ubuntu has a very solid server image that you can use. I haven’t touched it in a while (I’m a CentOS guy) but it’s a great place for someone who, as you mentioned, is a bit inexperienced.
If you’d like an in-depth overview of Linux distros (admittedly from a desktop perspective), have a look at this guide.
My top 3 recommendations for newbies looking for a server distro are:
- Ubuntu
- Debian
- CentOS