Currently, the help for every hooks inside the hook dialog box itself could be improved. :)
Let me explain what I mean:
Go into a repository and then to "Administration" -> "Hooks". You can see the following introducery text:
Hooks allow you to extend what Bitbucket does when the repository changes (for example, new code is pushed or a pull request is merged).
Select "Jenkins" as an example hook. A dialog box opens and you can see the following:
Endpoint Module name Project name Token
What I miss here is a short(!) explanation what Jenkins is (I know it, but other may not) and a link to its project home page. This applies to other hooks as well, of course.