To move down one level to a subdirectory:
cd Firstyear
This moves you down one level from your current directory to the subdirectory Firstyear.
To move up one level of the directory tree:
cd ..
Every directory contains a hidden directory .. (dot dot) that is a shorthand name for this directory's parent directory.
Using this shorthand name enables you to move up the directory tree very quickly without having to enter long pathnames.
To move to another directory using a relative pathname:
cd ../Secondyear
This moves you up one level in the directory tree and then moves you into the subdirectory Secondyear.
To move to a directory using a full pathname:
cd /home/physics/ercy04/ProjectX
This moves you to the directory ProjectX which is in the home directory of the user ercy04.
To go directly to your home directory:
cd