As I've been taking up curtains on the machine, I've been thinking how I've seen a couple of blog examples on how to do this the wrong way. So I thought I'd do this little sample to show you how it works.
First fold your edge to the back once and press.
Then make a 2nd wider fold along the line you want the hem to finish. Press.
You might want to enlarge this photo so you can see this next fold. You want about ¼" of the hem showing.
If you've ever wondered why the hemming foot has that piece of metal in the middle, it's so you can rest the fabric against it close enough just to catch it with the sideways stitch.
It should look like this.
Then fold back to the finished way and press. If you click on the photo below and look closely, you'll see the little hemming stitches. Now if I'd used a matching thread these wouldn't show at all.