Jerome,
there are a lot of Turks Head Knots on internet and in the different books.
If you have a local library you might find some there and otherwise they can order some for you from other libraries. (Buying knotbooks is good but can get expensive when you go for books like the Ashley Book Of Knots.)
If you tie a 4 bight, 3 lead T(urks) H(ead knot) you can make it longer, (give it more bights) by braiding it a little more before you start doubling.
Make the 4b, 3l TH and slip in over your hand, (make the knot bigger by pulling more string through if needed.)
On the top of your hand you now have three strings, 2 of which are fixed at their other end, one which is loose at the other end. With those you can braid, as with all sets of three strings. When the knot is long enough, you start doubling as you would do with any TH.
I hope you understand this. Otherwise, go looking for TH's in books and on internet.
Willeke