After a year or more of writing and researching you attach the Word file of your final manuscript to an email, and press SEND. The book is finally on its way to the publisher.
In the next few weeks and months you may be working with the publisher's editors and beginning book promotion.
There's a tendency now to forget about the original Word file. Don't do it!
Instead, save the file to CD. Put one copy in a safe place offsite. Keep a second CD on file in your office. A third copy of the file goes on your computer. Rename the file "Second Edition." Over the next year or so, you will inevitably find things in the manuscript that you want to correct, rewrite, or delete. As you find these things, make the changes in the "Second Edition" file you just saved.
When the publisher comes back to you in 18 or 24 months and asks you to prepare the second edition, you will be ready.