If you are starting a Linux server, might be good to drop by Udemy, Stack Social, etc., and find some classes on Linux if you don’t know Linux commands. You’ll want to know commands if you intend to use a gui-less server operating system. You can also install the gui version (desktop) of Ubuntu and it can still function as a server. The nice thing about Ubuntu server is the reduction in overhead from not needing to install/run the GUI, but you need to know commands or you may be a little lost.
It also depends on what you want to do with the server. Setup an email server, a router/DHCP server, a firewall, an internet Proxy Server, a NAS, file/media server, backup server? For each of these specialties, or all of them, you’ll want to learn more about the functions related to installing, administering, and supporting them or ask specifically how you install one of those once you get the server going.
If you have questions like:
How do I log in?
How do I install a package in Linux?
How do I setup a RAID with mdadm?
those are more specific questions you can ask here as well.
Here’re some links I used when starting out:
How to Create a NAS with Ubuntu Server – https://www.youtube.com/watch?v=-5Z_-3EBIHE&feature=youtu.be
Creating a NAS – https://docs.google.com/document/d/1hFw1YnH9s-1Y9M4VPLgPOOjm1iH6PJOHefg5NhGC4oA/edit?pli=1