First, make sure you ONLY use this link: http://videodropper.ep.io/ to access this resource. You may end up in a NSFW site otherwise, like I did!
Second, you need a Dropbox account. You can get a free account at dropbox.com. If you are in the dark, Dropbox allows you to backup files from your computers and access them on the cloud. Videodropper will take a Youtube video, download and convert it, and put it in your Dropbox folder.
Once you sync them, you just drop a YouTube URL and it does the work for you. Then you can access these files from Dropbox at your convenience. You are limited by your space on Dropbox, although you can download the videos, then delete them on Dropbox, or just pay for a larger Dropbox account. Pretty good resource!