NB. I've only used round cord for ease but Gerd's tutorial uses flat leather thong.
Its worth while practicing this first, particularly so you can get your hole size just right. Id' strongly recommend putting a point/taper on the ends of the leather strip and also not to wet the first inch or so, its a pain to feed through the holes otherwise.
OK here goes:
NB. Loop round once then feed through second hole
Once everything's all tightened up you can trim the excess and give the whole thing a bit of a whack with a hammer to flatten it out. Obviously the holes can be a little closer together too, this was just for clarity...honest :-P
Hope this helps.