Like for example when they choose a certain choice (page), they can earn Endurance +1 in their stats?
And if they choose otherwise they won't get the point.
see this link:
http://textadventures.co.uk/forum/quest/topic/psoh-wmvhugkpz_ttsvdqa/making-an-object#d0ec0ac9-7fff-45b3-a630-c700f558b8d1
and there's also this link too (leads to more links, that explain about Attributes, 'if' scripting, and coding in greater detail):
http://textadventures.co.uk/forum/general/topic/ljjm32av4e2t9ot49k478g/help#710be61e-eae1-4af1-8363-520cc718ba1c
ask if you need help about anything