You can define a file or directory by its location in relation to your current directory. The pathname is given as / (slash) separated list of the directories on the route to the file (or directory) from your current directory.
A .. (dot dot) is used to represent the directory immediately above the current directory.
In all shells except the Bourne shell, the /~ (tilde) character can be used as shorthand for the full pathname to your home directory.