The Concept: Voting is a way for users like you to have a say when it comes to tagging. There's always a dilemma when it comes to user input: on one hand, the more that users contribute, the better, but on the other hand, it's so easy to get false or malicious data, either intentionally or unintentionally. GreyHen's voting system was designed to solve this problem; it lets everyone have a say, while not allowing small portions of false data to be harmful on their own.
Getting started: To make a vote, simply view any file. Near the bottom of the page will be a list of tags - next to most of these is a red "X", which you can click to start a vote to remove that tag. Below all the tags is a text field, where you can type a tag that you think belongs on this file - just type it and hit enter, and the vote will start. You'll know the vote has started because, directly beneath the section with all the tags, a section labeled "Ongoing Votes" will appear, which shows all of the votes involving this file. Next to each of these is a check and an X; by clicking on these you can vote for or against the tag in question.
Going Further: Adding tags to random files you find is all well and good, and lets a file change long after it enters the database, but unless you stumble across a file people are voting on, you're not really contributing to other votes much. To do that, visit the voting page. The most important part of this page is the "See all ongoing votes" link - this link will show you all ongoing votes that you have yet to vote on. This lets you perform many votes in quick succession, which is one of the best ways to attain...
Levels: Now that you've learned about the main links on the voting page, it's time to learn about this page's other cool feature: levels. You have no levels on a new account; to make one, type one of your favorite tags into the text field below the main links and hit enter. Voila, you have a level! It's at level 0 for now, though. To level it up, you'll need to gain experience - mouse over the bar to see how much - and to gain experience, you need to vote. By voting correctly on a given tag, you'll gain experience in it, which will let you level up, which will make your votes on that tag count for more; after thousands of votes, you'll cap out at level 100! The two buttons next to each level are the "Ongoing Votes" and "Remove" links. "Remove" gets rid of any progress you have with that level; be careful, as this cannot be undone, and if you decide to use that level again, you'll have to start from scratch. "Ongoing Votes" shows you all of the votes currently in progress regarding that tag - this is a great way to see new files with your favorite things on them!
Important Note: If you have a filter enabled, the voting page will never show you a file which violates that filter. However, keep in mind that many of the files being voted on do not have a complete set of tags - if an image hasn't been tagged with "gore" yet, your filters won't remove it, no matter how bloody it is. As such, exercise caution when voting - moderators will try to make sure anything too strange gets tagged as soon as possible, but don't rely on it. With that out of the way, though: happy voting!