This sets the size of the font.
Height and width are measured in points, the traditional printing industry unit of measurement, which is 1/72nd of an inch.
Usually, you will only be interested in setting the height of the font. To set the height:
The width of the font will be its correct width proportional to its height, if you leave the width set to zero. You may wish to alter the width of the font to create a special effect. This can result in unpleasantly distorted type if taken to extremes. There are two things you can do with the width option:
As a rule, you will only get usable results condensing serif fonts 10 per cent or less, and expanding or condensing sans serif fonts by up to a third.