Basically, there's several ways of turning heels in knitting.
The gist of a top down one is explained fairly well in the pattern below:http://www.knitty.com/ISSUEwinter02/PATTfuzzyfeet.html
Basically, you start the tube for the top of the sock, take a portion of your stitches, and then knit on only those stitches to make a flap. The tube stops about where your foot begins and the flap goes from that point down almost to the heel, and then you decrease it so it'll hug to the foot. Then you pick up stitches from the sides of the flap and knit around, decreasing on either side of your gusset (that's the triangular area on either side of the sock.)
Another option is a short rowed heel. In that case, you're knitting back and forth without doing a full row to shape the heel. Searching for "short rowed heel" should give you some information about it.
A lot of these concepts could be translated into crochet. For a crocheted sock, you'll want a fairly thin yarn due to the thickness of the standard crochet stitches. You'll want to start with a small patch (about an inch) and widen it into a tube that will fit over the widest point of your toes. Now, crochet in a tube up to the required hieght, and finish it. You've just made a tube sock. A stretchy ribbing like pattern would help the fit.
Sizing: The important points on a toe up sock is the point where you stop increasing (when it will fit over the widest point of your toes), the point where your foot stops and your leg begins (that's where you start the heel), and the point where your leg starts to widen (that's where you worry about adding stitches to fit the leg.)
You might want to try to borrow a copy of "Folk Socks" to see the neat heel and toe information there. You might also be interested in nalbinding - which, as I remember, is how you made Viking socks. Here's the first link I found about it.http://www.norsefolk.com/clothing/nalbinding.html