/cmd-vel is of the geometry_msgs/Twist message format. The message structure can be found at http://docs.ros.org/melodic/api/geometry_msgs/html/msg/Twist.html.
/odom is of the nav_msgs/Odometry message format. The message structure can be found at http://docs.ros.org/melodic/api/nav_msgs/html/msg/Odometry.html.
Not all the fields are necessary in the case of our robot base since our robot is a 2 degrees of freedom robot.