Don't worry. When you are downloading a particular torrent, you are also uploading that torrent at the same time. The parts of the file(s) that you have already downloaded are uploaded to other peers. This is normal, and it's how the protocol works. There is no "shared directory" setting as with other peer-to-peer applications. If you have a certain file (or files) that you want to make available to others, you must first create a .torrent file and upload it to a server, and then seed the file. See the section How do I create a new torrent (share a file I have with others)? for the detailed procedure.