If you haven't already, you might want to read the first few articles in this series:
Homepage
The Vanilla homepage is set via the layout section of the dashboard settings:
With the exception of some very custom themes, all Vanilla landing pages will point to one of three things, discussions, categories, and best of), this determines what that landing page (home page) points to. You can read more about this here: Customizing Your Forum's Appearance - Vanilla Success
Categories
Categories are how Vanilla organizes discussions within a community. Categories can be added, edited, deleted, sorted, and tiered via the Dashboard. Every discussion is placed in one (and only one) category. Read more about categories
Recent Discussions
A list of all discussions from across the entire forum, or within the current subcommunity.
Activity
Activity is a stream that displays all recent member activity such as; who has joined, who has changed their picture, status updates, etc. You can choose who can see this via Roles and Permissions.
My Bookmarks
Bookmarks or My Bookmarks are discussions that have been starred (clicking on the star icon next to a discussion). Bookmarks are added to the Bookmarked Discussions Box in the Panel element (sidebar). Bookmarks are used to make following a favourite or important discussion, easier. Users can choose to be notified via pop up or email when other users comment on their bookmarked discussions.
This will only populate if the user has bookmarked at least 1 discussion.
Does not appear to guests, or users with no bookmarks.
My Discussions
A list of all discussions the currently signed in author has authored.
This will only populate if the user has authored at least 1 discussion.
Does not appear to guests.
My Drafts
A list of all discussions the currently signed in author has authored and saved as draft, but not yet published.
This will only populate if the user has authored at least 1 discussion.
Does not appear to guests.
Help
A link to the Knowledge Base associated with the community.
Only appears if the KB option is enabled and the current user has permissions to view.
See main article on KB
Unresolved
A list of unanswered questions that the currently logged in user has permission to see.
Only appears when the Q&A addon is enabled.
See main article on Q&A
Best Of
One of the easiest ways to showcase the best content in your community is the Best Of feature. Members of your community vote on the best content, as does your moderation team and staff, and only the best content appears. Also you can give your staff the ability to push certain content to the Best Of page too, which will constantly be refreshed as new stuff gets added. Finally, you can even set the Best Of section as your homepage.
TLDR: A list of posts that have received at least 5 points (that can be configured).
Only appears when the reactions addon is enabled.
To learn more about best of, read the Reactions article.
Groups
Groups is an optional addon -- read more about it in the main Groups Article.
Only appears when the groups addon is enabled.