If you're new to Fort?GL
http://docs.sun.com/app/docs?q=UDS+reference or F1
If your question is about how to automatically generate code (including GUIs) from the BTD files those API are not documented but you may start from importing (using fscript) the plan "qqAllForteProjects" and start from the class qqcf_RepositoryClient.
Hope this help.
Cheers.