You can read about GHC in the GHC User Guide. The chapter about ghci will probably be of particular interest. The GHC Library Documentation describes the functions available as part of the standard library.

ghci quick start

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.