Here is a great illustrated guide by Nick Carlin "So you want to be a chess engine bookmaker"http://dl.dropbox.com/u/14906951/So%20you%20want%20to%20be%20a%20chess%20engine%20bookmaker.pdf
And here some clear instructions:
For the basic steps of creating a ctg book:
1. Start with a database of games that you want to use to make your book.
2. Create a new book in Fritz by selecting FILE/NEW/OPENINGS BOOK - call it anything you like.
3. Open your new book by selecting FILE/OPEN/OPENINGS BOOK and selecting the new book you created earlier.
4. Now import the games from your database by selecting EDIT/OPENINGS BOOK/IMPORT GAMES and navigating to your database.
5. There is a dialogue box which you need to tick against. "Games" is the number of games you want to import. Default is all games are selected so leave this. "Length" is how deep the lines will be in the book. Choosing "ECO-relative" plus a number will make the main line variations longer than the oddball side variations. If you pick "Absolute length" and a number, it will make all the variations the length you chose, regardless of whether the variation is a main line or side line - so book will be deeper. "Include variations" is important if some of the games from your database contain commentary in the form of sub-variations, but can be left un-ticked.
6. When you're finished with these settings, click "OK". You'll see a progress bar appear, keeping you posted as to how close Fritz has come to completing the, you'll see a menu of moves where the empty book had been and a small window saying "x new positions" (this tells you how many positions total are in the new tree). Click OK, and you're finished.
To manually edit the book here is a brief pointer: Go into Fritz and do File/Open/Openings Book and select the book you want to edit. Then select the Openings Book tab on right hand side of screen. Basically you can either a) add a new move to the book, To do this right click somewhere in that book area (not on a move just in empty space) and tick Allow Move Adding. then when you play back through a game and want to add new line, just make the move on the actual board and then select new main line from the options. This will then have added the move to the book.
b) change the 'weighting' of an existing move making it more/less likely to be chosen. This is shown in the Prob / % column. To change it right click on the actual move itself and do change weight. The value is from -125 (very unlikely to be picked) to +125 (very likely to be picked). You can change these manually to any value. Actually this is what the automatic book learning does based on whether games are won or lost - but this is how you do it manually.
c) or mark moves either red (means they won't be played ever) or green (mean they will be picked, with a probablility given by the % column). To make a move red right click on it and select Don't play in tournament To make a move green right click on it and select Main Move. You might want to make a move red if you find that at some point in the book line you had a negative evaluation and therefore you can mark that move red so it won't be played again