If you're using a sock, you'll need to cut the toe off. (It should look like a leg-warmer when you're done). If you're using a leg-warmer to begin with, you can skip this part.
This is what you're aiming for.
Next, roll the top of your sock downward. Continue folding over until you have a fabric donut, basically. (*Hint* this is the same motion you'll use later on, too)
If you haven't done so already, now is the time to put your hair in a ponytail. Remember that where you anchor the ponytail is where the middle of the bun will be.
Slide the sock around the base of the ponytail. Fan your hair out so that it is covering the sock, ends on the outside. Then, slide the donut to just before the end of your shortest layer.
Using the same motion as you did when rolling your sock, tuck the ends of your hair downward, so that the loose ends are eventually wrapped around the donut and no longer visible and/or loose.
Continue rolling until you reach your head. If, like me, you have really long hair, it might take a while. Once you've reached the base of the ponytail, wrap any loose ends around the base of the bun.
Secure your bun to your comfort level. Sometimes you don't even need a hair tie, sometimes you need an elastic, sometimes you need all of the above + bobby pins and hairspray.
This hairstyle is simple & versatile. It's also much harder to demonstrate than it is to actually do it in a mirror, hence the ridiculous faces I was making (sorry!)