For a single font, e.g., foo.ttf:
$ mkdir -p ~/.fonts
$ cp foo.ttf ~/.fonts/
+
+ One can run fc-cache to speed up the use of fontconfig.
$ fc-cache
+ For Windows users, one can go to the C:\windows\fonts
+ folder and use File -> Install New Font from the pull-down menus
+ to install the font.
+
For a new font directory, e.g., /Library/Fonts, add a new <dir> element
<dir>/Library/Fonts</dir>