someone asked something similar recently but they seem to have disappeared so I'll post my own version of the question.
I'm using bp-social theme but it doesn't really matter, they all perform the same:
if you click on a link to a group (from a list of forum posts, for example) it takes you to the group "home" page (normally the activity stream) with sub-headings to navigate to other group sub-pages, such as members and forum, additionally admin and send invites and calendar depending on your role, other plug-ins etc.
You can link to the group home with
Is there a way to link directly to one of the sub-pages, eg to go directly to the forum for example?
I'm talking about somehow embedding the target in the link so that you could set up alternative navigation to take you directly to the individual pages, rather than a one-off permanent change of the 'home'.