I have to say that it is very easy to use the tool but a bit more difficult to master it. When you first get started the cord is a little lumpy. After some practice it starts to get better. I have embedded a tutorial video below that shows the technique. I didn't produce the video. I didn't think was skilled enough to do it justice. The teacher in the video does a good job of showing how it works without getting too wordy.
A lucet is a tool used in cordmaking or braiding which is believed to date back to the Viking and Medieval periods, when it was used to create cords that were used on clothing,or to hang items from the belt. Lucet cord is square, strong, and slightly springy. It closely resembles knitted I-cord or the cord produced on a knitting spool. Lucet cord is formed by a series of loops, and will therefore unravel if cut. Unlike other braiding techniques such as kumihimo, finger-loop braiding or plaiting, where the threads are of a finite length, lucetted braids can be created without pre-measuring threads and so it is a technique suited for very long cords.
Archaeological finds and a literary description of lucets strongly suggest that its use declined after the 12th century, but was revived in the 17th century. Its use waned again in the early 19th century.
A modern lucet fork, like that pictured, is normally made of wood, with two prongs at one end and a handle on the other. It may also have a hole through which the cord can be pulled. Medieval lucets, in contrast, appear to be double-pronged, straight-sided implements, often made of bone. Some were shaped from hollowed bones, left tubular, presumably so that the cord could be drawn through the centre hole.[Source Wikipedia]