To understand this, you must first learn about the parts of the letter. There are three parts of a letter that help determine which classification the font falls into. Serifs are decorative lines that are added at the end of the strokes of some letters. Letters that do not have serifs are called sans serif . The stroke of the letter can be thick or thin.
Some fonts have uniform strokes and some have variations in the thickness of the strokes.
All of these things - serif, fillets and stroke need to be considered when determining which classification a font fits into. Each classification of font is used for different purposes. Here is a chart which explains. So - now you're all set to create something wonderful, and you know just what font will suit your purpose. A font file must be stored in the system folder of your Macintosh in order for you to be able to use it.