Custom URLs (Tools=>Options=>HTML)
Use this area to enter URLs of web pages that you want to appear on the Custom URL menu that GSAK displays when you right-click on a waypoint in the database view. Several URLs are provided by GSAK, but you can add your own by following the format used in the default entries in this field.
If you prefix a custom URL with ! (exclamation mark), that URL link will show in HTML pages produced by GSAK
Custom URLs for child waypoints should be prefixed by "Child_" (without the quotes) more information. Any "Child_" custom URLs must be placed at the very end of your list
You can use any of the special tags to generate your custom URLs
This feature also supports sub menus for grouping of custom URLs. For more information see this link
To maximize the use of URLs you may want to take a look at the URI help topic.