I don't get this sentence in the manual: "All activities start, continue for
a while and then finish: however, no activity ever runs on for more than a
single turn." If they don't run for more than a single turn, what does it
mean to say they continue for a while?

What this means is that an activities spans some fraction of a turn -
or, put another way, that an activity can continue *within* a turn but
not from one turn to the next.  Borrowing an example from the manual,
suppose the game prints this in response to the players "inventory"
command (annotated with output line numbers):

(1) You are carrying:
(2)   a rusty lantern
(3)   your spell book
(4)   3 Scrabble tiles (A, G and M)
(5)   a featureless white cube

The activity "listing contents of yourself" is continuing throughout the
time that lines 1-5 are being printed, but doesn't continue past the end
of the turn.  (If the player issues another inventory command in the
following turn, the same activity would repeat within that turn.)

news:rangk.6391$2N2.2052@fe091.usenetserver.com...

This makes sense to me now. I'm finding I wish the manual was written in the
same way that answers here are presented. I think it would make learning
Inform a much quicker process.

Of course, if that were the case, an entirely different group of people
would make the same complaint. ;)

Skinny Mike