A change log entry starts with a header line that contains the current date, your name (taken from the variable
add-log-full-name), and your email address (taken from the variable
add-log-mailing-address). Aside from these header lines, every line in the change log starts with a space or a tab. The bulk of the entry consists of items, each of which starts with a line starting with whitespace and a star. Here are two entries, both dated in May 1993, with two items and one item respectively.
1993-05-25 Richard Stallman <firstname.lastname@example.org>
* man.el: Rename symbols 'man-*' to 'Man-*'.
(manual-entry): Make prompt string clearer.
* simple.el (blink-matching-paren-distance):
Change default to 12,000.
1993-05-24 Richard Stallman <email@example.com>
* vc.el (minor-mode-map-alist): Don't use it if it's void.
(vc-cancel-version): Doc fix.
One entry can describe several changes; each change should have its own item, or its own line in an item. Normally there should be a blank line between items. When items are related (parts of the same change, in different places), group them by leaving no blank line between them.
You should put a copyright notice and permission notice at the end of the change log file. Here is an example:
Copyright 1997, 1998 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification, are
permitted provided the copyright notice and this notice are preserved.
Of course, you should substitute the proper years and copyright holder.