One quant is about one inch = 2.54 centimeters
If you want to make a character that is 1.8 m high,
he shoud be 70 quants high.
In the end, you can choose whatever sizes you want,
there is no build in "scale".
But a lot of people use this scale for objects.
(comes from the dimensions in the old Quake games)
Best is to place a reference character (that template wizard for example)
into the level, so you always see if other objects and
level-architecture are scaled correctly.
You can also see the quant dimensions when editing in MED.
On the bottom right. So you can already estimate how
big it will be in WED at the normal scale 1.