I am trying to learn ROS and so I was looking for some guide or tutorial series. I already managed to set up ROS Kinetic on a Raspberry Pi and ROS Noetic on a Ubuntu VM. I am quite experienced in Python and just need to learn ROS. Where is a good place to start. All the places I looked at were paid. I also have a basic robot setup with a L298N, 2 DC motors, and a camera.
In addition to the ROS tutorials already mentioned by Akhil Kurup, Robotis has a list of resources here. There are YT videos and a free e-book. Some of them are centered around their Turtlebot kit, but there are also general ROS info.
The official ROS tutorials are the best place to start. If you go through each of them (shouldn't take too long given your skill set), you will learn all the basics needed to start using widely available complex packages!