You go the Gallery Contest site, like this one:
http://www.photocamel.com/gallery/sh...ry.php?cat=615
And you should see a bunch of thumbnails down the page. These are the entries. Under each should be the word
Vote as a link. Click it and you will be voting for that image.
Currently you can only vote for one image. If you do not see the word Vote under the images, then either voting has not started, or you have already voted for an image. if the later, above all the image thumbnails, there will be an option to Clear your Vote. If you use that, the vote options under the thumbnails will be there again.
Hope that helps ya.