How To Decode A Broadcast

Let's say you receive a broadcast that sounds like this:
Octagon Octagon Octagon 18 7 1 16 23 9 20 35 9 23 3 28 0 20
Decoding it is simple (assuming you've been given the codebook). Here's how it works!

Octagon

Many numbers stations have their own unique opening sections. All automatically generated transmissions from Octagon 8 begin with the word "octagon" spoken three times. It does not contain any information about the message contents.

Page Number

Immediately following the word Octagon is a number indicating which page of the codebook needs to be used in order to decode the message. You can find the page numbers at the bottom of each page of the codebook PDF. In the above example, page 18 is mentioned. Pull up that page in your codebook PDF and it should look something like this:

Message

After the page number, the contents of the message are read aloud. Starting on the top left of the code book page, write each recited number above each code number, proceeding to the end of the line before wrapping to the next line.
07 01 16 23 09 20 35 09 23 03 28 00 20 <-- Numbers from the message.
26 23 31 02 19 06 04 31 32 05 02 13 06 <-- Codebook numbers.
For each number you wrote, subtract the code number under it. In the above example, we get:
  07   01   16   23   09   20   35   09   23   03   28   00   20  <-- Numbers from the message
- 26   23   31   02   19   06   04   31   32   05   02   13   06  <-- Codebook numbers
 -19  -22  -15   21  -10   14   31  -22   -9   -2   26  -13   14
Looking at the bottom of the code book page, we see the mapping from number to letter. If we apply this mapping to each number we see that -19 is H, -22 is E, -15 is L, 21 is also L, -10 is O, and so on, giving us our final message:
H E L L O E V E R Y O N E