The purpose of this website is to make it easy to add subtitles to Yotube videos.
To add a movie you have to specify the Youtube ID (found in the url of the video) and upload the file for the subtitles.
A good place to find subtitle files is OpenSubtitles.org, but it is up to you where do you take them from, as long as they are in SRT format.
Here is what you can do:
The website now supports only a small group of languages, but more languages will be added in the future.