The connection between the variables and the terminals is a mechanism known as a production. Each production will convert a variable into another set of terminals and variables. There may be more than one production associated with a variable and usually there will be more than one. The trick to the mimic functions is using the data to be hidden to select the productions. All other words including punctuation are treated as terminals.
Spaces are the separator between terminals.
The slash separates the different productions and the equals sign is used to join a variable with its productions. Two slashes signify the end of the set of productions for a variable. These numbers are not productions, but the probabilities that govern the preceding production. They are also approximate, although I'm not going to bother to describe why right here. The answer is in the tech report on mimic functions.