NotebookDirectory[] gives the directory of the current evaluation notebook. NotebookDirectory[nb] gives the directory for the notebook specified by nb.
SetDirectory["dir"] sets the current working directory to dir. SetDirectory[] sets the current working directory to your "home" directory.
DirectoryName["name"] extracts the directory name from the specification for a file.
CreateDirectory["dir"] creates a directory with name dir. CreateDirectory[] creates a directory in the default area for temporary directories on your computer system.
$BaseDirectory gives the base directory in which systemwide files to be loaded by Mathematica are conventionally placed.
RenameDirectory["dir_1", "dir_2"] renames the directory dir_1 to dir_2.
$UserBaseDirectory gives the base directory in which user-specific files to be loaded by Mathematica are conventionally placed.
DeleteDirectory["dir"] deletes the specified directory.
CopyDirectory["dir_1", "dir_2"] copies the directory dir_1 to dir_2.
Functions for manipulating files. Different operating systems have different commands for manipulating files. Mathematica provides a simple set of file manipulation ...