I initially used Mastering ROS for Robotics Programming - Third Edition
(I technically used the second edition back in my day, but I suggest using the third edition).
I quite liked that book. If memory serves, it started with some basic terms, then it went into URDF and you followed some steps to make a basic robot in Gazebo (the simulation program). Then you added sensors/controllers to that simulated robot, teaching you some basic stuff about URDF and simulations.
That's honestly where I stopped (in that book), because I had professors to help me with some more basic ROS stuff. However, it's a great way to be able to create and control (with keyboard teleop for instance) some simple robot that you've made in a simulation.
I personally like that way of starting with ROS, since it's a lot more "hands on" (even though everything is in simulation). You want to make some cool looking robot (in simulation) with an IMU, 3 lidars and a camera or 2, that book helps you do that. It's visual, which gives you some more satisfying results.
There's of course also the emanual for Turtlebot3. You don't actually need a Turtlebot3 for it, it has a chapter on simulations (just how to start it though, no actual knowledge) and you can run SLAM/navigation perfectly fine from the simulation.
Hopefully after that you'll have some understanding of ROS to ask specific questions (I get it though, ROS is hard to learn as a beginner). Since the more specific the question, the easier it will be for us to help.