The value is exactly that - a value.

So if we have an object called "gold", we can have a property called "amount", and have the property value set to how much gold is held - say "5".
Or, we could have the object called "sword", and give it the property "power" with the value of "10"... Which can effect combat/story events.
You can easily multiply any number - just set a variable.
To add two numbers together you do:
3 + 5
To subtract:
3 - 5
To multiply:
3 * 5 (Remember, x is a letter - not a mathmatical symbol.. In maths it's usually not even written - unless you're pre-algebra)
To devide:
3 / 5 (Something like a fraction - which is exactly a devide just not worked out yet to an exact value - usually for aesthetic reasons, or the fact that it creates a number like pi - with no end.)
Properties work like variables:
For instance, setting the property <gold; amount=20> will give the property a value of 20.
Now, to use that - you can use the following:
msg <Hello - you have #gold:amount# pieces of gold!>
The powerful part comes from if you have also potions and scrolls etc, all using "amount".
You can get it to print out the following in about 3 or 4 lines - which you can also use for a million other objects:
"You have 5 gold pieces,"
"You have 10 yellow scarfs,"
"You have 15 tin cans,"
"You have 3 oranges,"
"You have 1 bottle of water,"
"You have 11 hats,"