Say you want to increase your melee damage.  Melee damage is based on both
Strength and Agility and are combined in a way that gives preference to the
weaker.  If you are very strong (20 Strength), but clumsy (6 Agility),
a pairing of these stats will favor a value closer to 6 than to 20 --
definitely less then the average of 13.

If you want damage, you are better off having 13s in both stats.  Note that
13 and 13 are the same total as 20 and 6.  Stats are based around 13 as an
average stat.  Values lower than 13 may incur negative bonuses.

In regards to skills, the stat pairing modifies your "skill level". For 
example, say you have a "Good" skill in kick but you have a below
average Strength/Perception pairing, your kick skill will actually be
lower than your skill knowledge indicates.

It is important to note that skill level does not equate to damage for
skills that cause damage. For example, backstab's damage is still 
modified by the "damage" pairing of Strength/Agility while it's "skill"
pairing of Agility/Perception modifies the chance to land a successful
backstab.

You can `train' points from one stat to another to modify your character.

If you want exact details on the math, research the 'harmonic mean'.

Most Common Stat Pairing Calculation:

Scale = Range you wish the harmonic mean to encapsulate (i.e. for reanimate
and charm, the scale is 5 * level, meaning it can range from -50 to 50 based
on the provided stats)

Average Stat: 13

Max Stat: 25

scale * (2 * ((stat1 * 20) * (stat2 * 20)) - 
average_stat * (20 * ((stat1 * 20) + (stat2 * 20)))) 
/ ( (20 * ((stat1 * 20) + (stat2 * 20))) * (max_stat - average_stat))

There are a few variations on this - so this is not a perfect example of all 
stat pairings. 

See Also: Stats, Train

such as "spell" or "MUD Basics"