While the board index (forum home page) is packed with all kinds of information and links, the core of the interface (at least in the SMF default theme) normally looks something like this:
The forum name links back to the top of the board index.
If the category is collapsible (shown by the little arrow symbol), clicking the category name collapses or expands the category as appropriate.
The board name links to the message index for that board.
The board description describes the board's content, and may also include links to child boards and/or specify the board's moderator(s).
The New Posts and No New Posts icons in the leftmost column show registered members whether there have been any new posts to the board since they last read it.
The Mark as Read button enables registered members to mark all posts in the entire forum as 'read'.