(1) translate each letter of the message into a number, so a is 0, b is 1, c is 2, etc, and z is 25. (2) translate each number into binary, so 1 is 00001, 5 is 00101 etc. (3) translate each 0 into a and each 1 into b, so 10110 becomes babba etc. (4) write all the As and Bs under another piece of text (5) where there is an A under the letter, set the letter in normal type; where there is a B, set the letter in bold. So each letter in the hidden message appears as a pattern of five letters (either bold or normal) in a second message. It is a bit long winded to involve As and Bs instead of going straight from 0s and 1s, but that's how Francis Bacon did it.