The Abbreviations are really just a series of rules for letter substitution within any text written in the Latin script—having been optimized for English.
It's a kind of shorthand. But whereas most shorthands use a series of written symbols to approximate spoken syllables, this is an extended alphabet that comprises not only the standard 26 letters of the English alphabet but also a series of added letters that stand for common words or common sequences of letters. That's really it.