Linux admin course: Install Gentoo

Really just start by installing a distro you're interested in, learn how to set up a grid of terminals as your desktop background, then get in to doing any task you would normally through the terminal. What got me first interested in using linux years ago was the way you could make it look cool and messing around with different desktop environments, and I ended up being a unix admin for over a decade and run it at home wherever possible. I'd definitely do the self-exploration route, just find cool things you want to do on linux as inspiration and go for it. The great thing about linux is you can personalize it so it embodies whatever you love most about computers.

If you're doing this for potential career that's different, you'll want to learn more about managing daemons and security groups, disk provisioning, configuring services like httpd ssh autofs etc. Then get in to things like ansible and remote config/monitoring. At least from my experience, it's gonna depend on the employer. Kubernetes and enterprise containerized app solutions is what I'd be learning if I was about to enter the field again.