I'm not sure what BUMP means....exactly. I see it posted all the time but it never "bumps" anywhere. The top or anywhere else.
Over on the right hand side, if you select 'Messages' instead of 'Threads' you will see the latest posts for all threads. A 'Bump' will appear at the top of that list until the next posting, and folks might spot a now-buried thread.
In the old days, before sidebars and topics (and all of John's other masterful work), it would be the only way to spot an important, but older thread.
Don't feel bad - I've never bumped successfully either.