After reading an article about fonts, i tried the code and i am getting same results as show in the article but i can't figure out what those numbers XXX:XXX represent. Are they ascii values or what? What link should i read to understand about Typeface, GlyphTypeface mentioned in the answer?
Well - those numbers xxx:xxx is actual a pair - left number indicates unicode code point (i.e. unicode character code) and right side indicates the index to the glyph in the font file.
AFAIK, in very simple terms, glyph is a character representation i.e. how a character would look in a particular font/type-face. You may have a same glyph used for multiple characters and hence index in glyph tables is used. Typography is a involved subject and you can find a lot of material online - search for it. Here are few wikipedia pages that may get you started:
http://en.wikipedia.org/wiki/Glyph (see typography entry)
http://en.wikipedia.org/wiki/Font
http://en.wikipedia.org/wiki/Typeface
MSDN also has a lot of documentation (e..g http://msdn.microsoft.com/en-us/library/system.windows.media.glyphtypeface.aspx) but you need to get some basic background before that.