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There are a few different types of Braille;
Uncontracted - Grade 1:
consisting of the standard 26 letters, with punctuation, namely used by people beginning to read braille.
Contracted - Grade 2:
consisting of the same stard alphabet and punctuations and standard contrations. (The contraction are used as the amount of braille that can fit on a page is not the same as stardard text, they are used in public places; menus, signs and books.)
Grade 3:
used for personal situations, diaries and notes, although it has been known to appear in books. This isn't an official style but is often used nonetheless, its rather like shorthand in the idea that most words are turned into a small collection of letters.

Contractions 1;

http://www.braillebug.org/braille_deciphering.asp
http://en.wikipedia.org/wiki/Braille
http://www.omniglot.com/writing/braille.htm