You can read about GHC in the GHC User
will probably be of particular interest. The GHC Library
describes the functions available as part of the standard library.
You can run the interpreter from the shell by typing ghci. The interpreter provides its own prompt, allowing you to enter Haskell expressions, which are then evaluated.
There is a nice Haskell emacs mode if you are so inclined.
The interpreter also provides many useful commands. These commands start with a colon, :. Some of particular interest are:
You can see a list of commands with the :? command.