I believe this month's Threads has an article about making corners with these - check your local library if you don't have a subscription.
Meanwhile: Look in between the two "toes" of the foot (reminds me of a dirty joke...) and you should see a piece of metal shaped into a spiral, like a loosely-rolled up piece of paper or a seashell. Your fabric is supposed to go in that, and the spiral will fold the edge of your fabric over twice and stitch it down.
I've never used mine on organza, so I'm not sure how it will work, but here're some generic tips about using these things:
- they work much better on a straight, perfectly on-grain cut. If you are hemming a straight edge (which I assume you will be, with table runners), you'll want to pull a thread and cut. Don't tear the edge because it will make it a bit wavy and will also leave little threads sticking out of the hem.
- they hem from the *wrong* side. If your machine doesn't make a perfectly balanced stitch, you may want to try something else.
HTH. gabrielle