Popfont class derives from Area class and creates a widget which allows the user to select a font. Popfont widgets usually contain a button which, when clicked, pops up a dialog prompting the user to choose a font. This is all managed automatically by the widget and you don't have to do anything except putting the widget somewhere in your window layout.
You can set the title of the popup dialog using the Popfont.Title attribute on the Popfont object and you can get the user's selection by getting the Popfont.Font attribute.