First if you want to move your file to another folder, do it before you seed it.

After you post your torrent here, you need to download that posted torrent.

Then you open it in your usual torrent program and when that program asks where you want to save it you point it to the ORIGINAL file you made the torrent from.

Don't worry if it says it will overwrite the file, it won't (but you can make a copy to be safe). Then the prog will check that file to see that is the right one and then start seeding.

You don't have to do anything with the actual file. And if you need any more help, just shout