Squareworm is a nice font style that allows you to quickly give a casual, marker like effect to any text string.
To install the Squareworm font simply unzip the archive and put the font file (.ttf, .otf) into /Library/Fonts . Squareworm font integrates quickly into your system and you can easily access the custom glyphs though any text editing application.
Mac OS X comes with pre installed font styles and Squareworm will simply be added to your pre existent library. The process is managed through the Font Book application, where you can easily browse and preview your currently installed fonts.
To learn more about dealing with the Font Book application you can easily access the Apple support page HERE.