Admin panel settings determine whether votes, likes, or both are enabled:
These effects are available only for other commenter's comments. You can't vote for/against or like/dislike your own comment.
You can vote for/against and like/dislike other people’s comments, but you may do so only once per comment. These effects are permanent.
If the site’s administrator has set it up that these effects cost extra points (see, "Game Rules" tab in the admin panel), the buying-for-points dialog will be shown.
But if effects are free of charge they will be applied by a simple click: