Torrent Newbie

Hi, I have a question about using torrents.  I'm a newb with this so bear with me...
I have downloaded a few torrents from mousebits with Transmission for Mac.  I want to keep them available for others to download but after a while the file "times out" and gives me an error that the tracker is not available.  Does this mean it will not send the files to peers who want it?  I really want to give back, just I am having some newbie issues.

Thanks
Greg