Double pointed needles are used to knit tubes, like socks, when you don't want a seam.
I always try new stuff with leftover yarn, so I found what was left of what I used for a Christmas stocking last year.
This picture is about 4 or 5 rows into it. I had just about gotten the hang of managing all those needles.
I decided that this would make a good cover for the handle of my Calphalon tea kettle. It gets a bit too hot to hold on to.
Here's a closer look at the cover.