Note: I am not trying to be condescending, just noticing a pattern to your questions.
cd .. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< What does CD.. mean?
This is actually nothing too complicated, it simply changes the directory to the one that contains the current one. In Windows parlor: we go up, to the folder that is the parent of the current folder.
This is also not ROS specific in any way (Windows cmd.exe
supports the same command), and here are some links to some pages that may help to reduce the 'magic incantation' parts of command-line ROS:
There are countless more: linux command line tutorial.
In my experience, once people get to understand the Linux command line a bit, the 'magic incantations' in the ROS tutorials start to actually make sense.