The first 6 lessons of ROS tutorial for Husarion CORE2 are available here https://husarion.com/core2/tutorials/ros-tutorials/1-ros-introduction .

Instructions are created for ROSbot, but you can learn a lot if you have only CORE2-ROS.

Covered topics are:

1. ROS introduction
2. creating nodes
3. simple kinematics for mobile robot
4. visual object recognition
5. running ROS on multiple machines
6. SLAM navigation
7. Path planning
8. Unknown environment exploration

Check it out!