Start at the beginning. Install linux on a computer. I suppose this depends on how comfortable this person is with using a terminal and shell, but I started with an old laptop and a few hours of youtube videos on how to install arch linux. I took a lot of notes and a few more hours of actually installing arch. Jay’s latest video is great and it will dip your toes into LVM’s too. This will force a person to get more comfortable with using a bash prompt, and learn a few things about how linux works. If you want ease into it, I would install Ubuntu or Pop!_OS or Mint. These are all debian based distros and have a huge community behind it with a wealth of information. If you ever need help with any of these, a quick google search of the problem will inevitably lead to a solution. If you are looking for something closer to RedHat I would recommend Fedora, but Alma and Rocky are good too. Fedora doesn’t have as large of a community but with a little more digging (usually not much more) you can google answers for problems here too.
It’s not a bad idea to set up a remote server you can play with. Depending on your resources you can set up an old computer, raspberry pi, a virtual machine (requires no extra hardware), or even a cloud server(free options are available). Use this as a risk free playground. You can screw it up and restart from the beginning at any time. Learn to SSH into it. Setting up SSH keys is a good thing to learn too.
If you don’t care to read too much LearnLinuxTV is a great resource, Linux Essentials is a good starting point.
https://linuxjourney.com/ has a great program that is free. It’s all text but you can try everything out on your new linux install. It’ll progress through the command line, to how linux works and how networking works.
Reddit has r/linuxupskillchallenge that will walk you through a lot the material in the linuxjourney.com while also giving you real world experience. It’s all pretty basic stuff but will get you using the things you are reading about in a sort of classroom like experience. It is free, but more interactive, although a lot of reading too.
I would recommend buying Jay’s book Mastering Ubuntu server. Most of the material in this book is applicable to any distro, despite the title. It covers a lot of the basics and follows a natural progression through learning how to become an administrator. Plus it’s got some great projects to follow along with including ansible.
Then follow Jay’s Ansible series. It’s pretty thorough and after following along with that the website begins to seem much easier to understand.
Reading Linux Command Line and Shell Scripting Bilble is not a bad idea either. I bought mine but there is a free copy of the last edition available at https://z-lib.org/. There are numerous other great books available there.
That’s mostly how I’ve learned to get where I am at. I’m no linux admin, but it’s gotten me pretty comfortable with linux.