Haskell will be a vehicle to discuss programming in a pure functional language, and static, polymorphic type systems and type inference.
The Haskell lectures notes with a .hs extension can all be run in Haskell -- if you want to run them, download them, and if necessary rename them to have just a .hs extension (not a .txt extension).
The Haskell Prelude is a set of standard functions that come with Haskell -- the index (linked above) is a useful way to find out what is buit in.
"Haskell mode for Emacs" is a convenient way to run Haskell from the emacs editor, as well as letting emacs know about Haskell syntax. I wouldn't start with this right off -- figure out how to run Haskell just by itself first -- but you may well find it convenient after you're comfortable with Haskell.