There are two buttons below the article (if it's hubs you're talking about): one marks the article or hub up, the other down.
By marking a hub up, you will help to raise the score of said hub, where if you mark it down, the reverse is true.
Marking up would undoubtedly show you like the hub/article.
On questions, it is the answer that can be marked up or down, though here, the marking is immediate and shows both the total up marks in green and down marks in red.
Hope this helps and thanks for your comment on my hub today!