Get the size of a directory/file on GNU/Linux

Desktops such as GNOME, KDE, LXDE, XFCE offer an easy way to determine the size of a file or directory, right-click on the file in question, select properties from the context menu, but environments servers we dont like those mentioned above so it should resort to the CLI and make use of the du command which calculates the space occupied by a file or directory