When you try to upvote a question or an answer and you don't have enough reputation (15 points, it seems to me), a message occurs stating that your preference had been recorded by the system, but actually nothing happens.
Voting is a privilege you have to earn. If you don't have at least 15 rep points, you cannot upvote; and if you don't have at least 125 rep points, you cannot downvote. This is done in part to make sure you understand how the community works before you start judging its content. The page Privileges contains more information about other privileges you can get by contributing to this site.
If you don't comply with these restrictions, your vote will not be materialised. The vote is recorded internally, and it may be used by the developers as useful information. They track these kinds of actions, for statistical purposes. But, for all practical purposes, your vote will be useless. It will never be taken into account as far as what users can see.
You may find this meta post useful if you want some more details.