i can recommend you learn from google which os that you like but i recommend Centos because it had many how to in google then you can learn more from digitalocean how to
There are many sources where you can learn. I recommend to order a cheap VPS server with automatic re-installations and try to install and run scripts. Like install any free panel, after configure this panel.
You can also try to look to youtube videos, there are lot's of information.
You can use forums to learn about different OS and server installation with simple command lines to start with ,linuxquestions.org is one good forum to learn from.
In the beginning you also could install a control panel like VestaCP to manage your websites on a linux vps if you dont know how to setup and manage it from ssh.
trial and error is a good way of learning google can bring up almost anything vps related there's tons of information out there but get a test box with around 512mb ram and 10gb disk with unlimited reinstall's then just test different software try breaking it then sourcing the problem there's no better way to learn than hands on