Where you type in the location you download them to (drive, folder etc)
If you had them in a folder C:/Downloads and moved them to C:/completed, that's the information it needs. When you open the torrent file it needs to see the downloaded file already there so you may need to change the destination folder in your client. It's where you download to that need to be the same as where the actual audio/video file is NOW.
It should look and see that you already have it there, check it and then start seeding
If you have altered the file in any way, it won't match and will presume you are downloading a new one.
WARNING
Azureus asks you if you really want to download as it already exists and will overwrite the file. (I presume Utorrent does something the same). Clicking YES will get the client to check the file and, if it hasn't been messed with, will the go on to seed.
IF it has been altered, you will lose the original file as it will be overwritten by the new download (if in doubt, copy and paste the file somewhere else until you are happy it worked)
Hope that makes sense.