As Office Guy said, the correct definition of prepend would be "To prefix an expression with another". Which means to put in front of the other. The relative path means the path relative to the file you're working on. So if you are currently working in the root directory of your site, and you are trying to access something in the images/thumbnails/ directory within the site root, you will put images/thumbnails/ as the relative path. If the file you are currently using is in the images/thumbnails directory and you are trying reference something in the image/information/ directory, you would use ../information/. The ".." specifies that you are going up one directory. So in this case, the ".." specifies to go to the image directory.
