Ya, you have to first download it from DC and than just seed it as much as you can. Remember that it doesn't count as DL but only as UL. So, that's good for you.
You can only seed the torrent without DL when you put something of your's on DC (any music, movie etc). If you don't know how to do that than refer to the guides/tutorials in the site assistance section.
PS: Your ratio has improved a lot, so keep up the hard work and it will be paid off.

Hope this helps.