The original game, with human players, is played as follows:
One player chooses a person, place or thing (which should be known to all players). The others then, in turn, ask a question of the first; questions must be answerable with "yes" or "no". It's considered good form, however, to clarify a literal answer that would otherwise be misleading. For example, one of my friends recently asked me whether the person I was thinking of was in Rochester. She was actually in the town of Greece, our particular suburb, but I answered "Yes, she's in greater Rochester.
The great advantage of this game is that it can be played in almost any situation: In a car with one player driving, during a hike, sitting at home, via almost any online medium.