Hi,

1. Where all the packages should be locked? Should a folder ROCON appear after installing this? :

sudo apt-get install ros-melodic-ros-tutorials ros-melodic-geometry-tutorials ros-melodic-rviz ros-melodic-rosbash ros-melodic-rqt-tf-tree

1. Second turtle doesn't appear, I tried "rosrun turtletf turtletf_listener" command, it still doesn't work.

Thanks for help guys.