The game is playing on this page in an applet (so you may need to click on the game window before entering your commands). If you'd rather play it locally on your computer, you can download the platform-independent gamefile and an interpreter for your platform (Windows, MacOS, Linux, or something else). The advantage of downloading is a somewhat faster response time, cleaner UI, and being able to save your game and resume it later, but it is also perfectly playable as an applet on this page.
INTERACTIVE FICTION -- GETTING STARTED
"Okay, so what's this ? thingy?"
Good question. The ? prompt appears whenever it is your turn to tell
  the game what you want to do. Simply type in an imperative statement,
  like OPEN THE DOOR, or EAT THE SANDWICH, and press the Enter key. Also,
  articles aren't necessary: OPEN DOOR or EAT SANDWICH will work just as
  well. Occasionally, the game will ask you to clarify a command you've
  typed. For instance, if you type EAT SANDWICH, and there is more than
  one sandwich in your immediate vicinity, the game may respond, "Which
  sandwich do you mean, the ham sandwich or the bologna sandwich?" It
  is not usually necessary to retype your command -- simply answering the
  question is fine (HAM is a sufficient reply, for example.) Of course,
  you don't have to answer the question if you don't want to; if you're a
  vegetarian and don't want to eat either sandwich, you can type OPEN DOOR
  and the game will treat it as an all-new command.
Generally once you're past the introduction and the game has begun,
  you'll want to find out if the author has any special instructions for
  the game -- try typing HELP or ABOUT if a command hasn't been recommended
  explicitly by the game.
No matter how enthralling your initial location is, chances are you'll
  eventually want to go somewhere else. To do so, simply type the
  direction you want to go: GO NORTH is a perfectly acceptable command,
  but N will do the same thing, and is much easier to type. Most text
  adventures understand twelve directions: the four cardinal directions
  (N, S, E, W), four diagonals (NE, NW, SE, SW), UP and DOWN (which may be
  abbreviated U and D), and IN and OUT. (These last two may not be
  appropriate in many places: IN makes sense if you're standing next to a
  car, for instance, but not if you're standing all alone in a meadow.)
Pronouns such as IT are useful, but can be tricky. Usually, IT refers to
  the last object you used as a direct object of a command: if you type
  EXAMINE RHODODENDRON and the description is appealing enough that the
  rhododendron must be yours, TAKE IT is sufficient. Be careful, though,
  or you'll fall into the following trap:
 > EXAMINE FLOWER
  Which flower do you mean, the rhododendron or the chrysanthemum?
 > RHODODENDRON
  It's awful purdy.
 > TAKE IT
  Taken.
 > PUT IT IN BACKPACK
  Done.
 > CLOSE IT
  You can't close a rhododendron!
ALL is another useful word for when you want to PUT ALL IN BACKPACK or
  TAKE ALL FROM CUPBOARD; you can even go so far as to DROP ALL EXCEPT
  RHODODENDRON AND SANDWICH if you like.
Most interactive fiction these days has a reasonably impressive vocabulary;
  some words you might want to try are:
ATTACH GIVE PUT 
  CLIMB JUMP REMOVE
  CLOSE LOOK SEARCH
  DROP OPEN TOUCH
  EAT PULL TURN
  EXAMINE PUSH WEAR
You can also combine many of these verbs with prepositions: in addition
  to LOOK, you can LOOK AT, LOOK INSIDE, LOOK UNDER, LOOK THROUGH, and so
  forth.
There are also a number of special commands and abbreviations you should
  be aware of. In addition to the compass directions mentioned above, they
  include:
G: short for AGAIN, this repeats the last command.
I: short for INVENTORY, this produces a list of what you're carrying.
L: short for LOOK, this describes your surroundings.
X: short for EXAMINE, this provides a description of an object.
Z: short for WAIT, this causes a turn to pass without an action being
  performed.
SCORE: this tells how you're doing (sometimes)
QUIT: ends the game.
RESTART: restarts the game from the beginning.
RESTORE: restores a saved game (not available online.)
SAVE: saves your position in the game (not available online.)
This is only the beginning of what you can do in a piece of interactive
  fiction. Every game will provide additional verbs, rules and capabilities
  unique to that game. Feel your way around, try things as they occur to
  you, and most of all, have fun!
[Adapted from a document by Adam Cadre, at http://adamcadre.ac/content/if.txt]